Replace properties with flows

CHANGELOG.md

@@ -8,6 +8,8 @@
 - Add Meta and MutableMeta delegates for convertable and serializeable
 
 ### Changed
+- Descriptor `children` renamed to `nodes`
+- `MetaConverter` now inherits `MetaSpec` (former `Specifiction`). So `MetaConverter` could be used more universally.
 
 ### Deprecated
 - `node(key,converter)` in favor of `serializable` delegate

build.gradle.kts

@@ -8,7 +8,7 @@ plugins {
 
 allprojects {
     group = "space.kscience"
-    version = "0.7.2-dev-2"
+    version = "0.8.0-dev-1"
 }
 
 subprojects {

dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/properties/MetaProperty.kt

@@ -1,35 +0,0 @@
-package space.kscience.dataforge.properties
-
-
-import space.kscience.dataforge.meta.Meta
-import space.kscience.dataforge.meta.ObservableMutableMeta
-import space.kscience.dataforge.meta.transformations.MetaConverter
-import space.kscience.dataforge.meta.transformations.nullableMetaToObject
-import space.kscience.dataforge.meta.transformations.nullableObjectToMeta
-import space.kscience.dataforge.misc.DFExperimental
-import space.kscience.dataforge.names.Name
-import space.kscience.dataforge.names.startsWith
-
-@DFExperimental
-public class MetaProperty<T : Any>(
-    public val meta: ObservableMutableMeta,
-    public val name: Name,
-    public val converter: MetaConverter<T>,
-) : Property<T?> {
-
-    override var value: T?
-        get() = converter.nullableMetaToObject(meta[name])
-        set(value) {
-            meta[name] = converter.nullableObjectToMeta(value) ?: Meta.EMPTY
-        }
-
-    override fun onChange(owner: Any?, callback: (T?) -> Unit) {
-        meta.onChange(owner) { name ->
-            if (name.startsWith(this@MetaProperty.name)) callback(converter.nullableMetaToObject(this[name]))
-        }
-    }
-
-    override fun removeChangeListener(owner: Any?) {
-        meta.removeListener(owner)
-    }
-}

dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/properties/Property.kt

@@ -1,47 +0,0 @@
-package space.kscience.dataforge.properties
-
-import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.flow.MutableStateFlow
-import kotlinx.coroutines.flow.StateFlow
-import space.kscience.dataforge.misc.DFExperimental
-
-@DFExperimental
-public interface Property<T> {
-    public var value: T
-
-    public fun onChange(owner: Any? = null, callback: (T) -> Unit)
-    public fun removeChangeListener(owner: Any? = null)
-}
-
-@DFExperimental
-@OptIn(ExperimentalCoroutinesApi::class)
-public fun <T> Property<T>.toFlow(): StateFlow<T> = MutableStateFlow(value).also { stateFlow ->
-    onChange {
-        stateFlow.value = it
-    }
-}
-
-/**
- * Reflect all changes in the [source] property onto this property. Does not reflect changes back.
- *
- * @return a mirroring job
- */
-@DFExperimental
-public fun <T> Property<T>.mirror(source: Property<T>) {
-    source.onChange(this) {
-        this.value = it
-    }
-}
-
-/**
- * Bi-directional connection between properties
- */
-@DFExperimental
-public fun <T> Property<T>.bind(other: Property<T>) {
-    onChange(other) {
-        other.value = it
-    }
-    other.onChange {
-        this.value = it
-    }
-}

dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/properties/metaAsFlow.kt

@@ -0,0 +1,51 @@
+package space.kscience.dataforge.properties
+
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.*
+import kotlinx.coroutines.launch
+import space.kscience.dataforge.meta.*
+import space.kscience.dataforge.misc.DFExperimental
+
+@DFExperimental
+public fun <T> ObservableMeta.asFlow(converter: MetaSpec<T>): Flow<T> = callbackFlow {
+    onChange(this){
+        trySend(converter.read(this))
+    }
+
+    awaitClose{
+        removeListener(this)
+    }
+}
+
+@DFExperimental
+public fun <T> MutableMeta.listenTo(
+    scope: CoroutineScope,
+    converter: MetaConverter<T>,
+    flow: Flow<T>,
+): Job = flow.onEach {
+    update(converter.convert(it))
+}.launchIn(scope)
+
+@DFExperimental
+public fun <T> ObservableMutableMeta.bind(
+    scope: CoroutineScope,
+    converter: MetaConverter<T>,
+    flow: MutableSharedFlow<T>,
+): Job = scope.launch{
+    listenTo(this, converter,flow)
+    onChange(flow){
+        launch {
+            flow.emit(converter.read(this@onChange))
+        }
+    }
+    flow.onCompletion {
+        removeListener(flow)
+    }
+}.also {
+    it.invokeOnCompletion {
+        removeListener(flow)
+    }
+}

dataforge-context/src/commonMain/kotlin/space/kscience/dataforge/properties/schemeProperty.kt

@@ -1,31 +0,0 @@
-package space.kscience.dataforge.properties
-
-
-import space.kscience.dataforge.meta.Scheme
-import space.kscience.dataforge.misc.DFExperimental
-import space.kscience.dataforge.names.parseAsName
-import space.kscience.dataforge.names.startsWith
-import kotlin.reflect.KMutableProperty1
-
-@DFExperimental
-public fun <S : Scheme, T : Any> S.property(property: KMutableProperty1<S, T?>): Property<T?> =
-    object : Property<T?> {
-        override var value: T?
-            get() = property.get(this@property)
-            set(value) {
-                property.set(this@property, value)
-            }
-
-        override fun onChange(owner: Any?, callback: (T?) -> Unit) {
-            this@property.meta.onChange(this) { name ->
-                if (name.startsWith(property.name.parseAsName(true))) {
-                    callback(property.get(this@property))
-                }
-            }
-        }
-
-        override fun removeChangeListener(owner: Any?) {
-            this@property.meta.removeListener(this@property)
-        }
-
-    }

dataforge-context/src/commonTest/kotlin/space/kscience/dataforge/properties/MetaPropertiesTest.kt

@@ -1,28 +0,0 @@
-package space.kscience.dataforge.properties
-
-import space.kscience.dataforge.meta.Scheme
-import space.kscience.dataforge.meta.SchemeSpec
-import space.kscience.dataforge.meta.int
-import space.kscience.dataforge.misc.DFExperimental
-import kotlin.test.Test
-import kotlin.test.assertEquals
-
-internal class TestScheme : Scheme() {
-    var a by int()
-    var b by int()
-    companion object : SchemeSpec<TestScheme>(::TestScheme)
-}
-
-@DFExperimental
-class MetaPropertiesTest {
-    @Test
-    fun testBinding() {
-        val scheme = TestScheme.empty()
-        val a = scheme.property(TestScheme::a)
-        val b = scheme.property(TestScheme::b)
-        a.bind(b)
-        scheme.a = 2
-        assertEquals(2, scheme.b)
-        assertEquals(2, b.value)
-    }
-}

dataforge-context/src/jsMain/kotlin/space/kscience/dataforge/properties/bindings.kt

@@ -1,32 +0,0 @@
-package space.kscience.dataforge.properties
-
-import org.w3c.dom.HTMLInputElement
-import space.kscience.dataforge.misc.DFExperimental
-
-@DFExperimental
-public fun HTMLInputElement.bindValue(property: Property<String>) {
-    if (this.onchange != null) error("Input element already bound")
-    this.onchange = {
-        property.value = this.value
-        Unit
-    }
-    property.onChange(this) {
-        if (value != it) {
-            value = it
-        }
-    }
-}
-
-@DFExperimental
-public fun HTMLInputElement.bindChecked(property: Property<Boolean>) {
-    if (this.onchange != null) error("Input element already bound")
-    this.onchange = {
-        property.value = this.checked
-        Unit
-    }
-    property.onChange(this) {
-        if (checked != it) {
-            checked = it
-        }
-    }
-}

dataforge-context/src/jvmMain/kotlin/space/kscience/dataforge/descriptors/annotations.kt

@@ -1,126 +0,0 @@
-/*
- * Copyright  2018 Alexander Nozik.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- *  Unless required by applicable law or agreed to in writing, software
- *  distributed under the License is distributed on an "AS IS" BASIS,
- *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *  See the License for the specific language governing permissions and
- *  limitations under the License.
- */
-
-package space.kscience.dataforge.descriptors
-
-//@MustBeDocumented
-//annotation class Attribute(
-//    val key: String,
-//    val value: String
-//)
-//
-//@MustBeDocumented
-//annotation class Attributes(
-//    val attrs: Array<Attribute>
-//)
-//
-//@MustBeDocumented
-//annotation class ItemDef(
-//    val info: String = "",
-//    val multiple: Boolean = false,
-//    val required: Boolean = false
-//)
-//
-//@Target(AnnotationTarget.PROPERTY)
-//@MustBeDocumented
-//annotation class ValueDef(
-//    val type: Array<ValueType> = [ValueType.STRING],
-//    val def: String = "",
-//    val allowed: Array<String> = [],
-//    val enumeration: KClass<*> = Any::class
-//)
-
-///**
-// * Description text for meta property, node or whole object
-// */
-//@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class Description(val value: String)
-//
-///**
-// * Annotation for value property which states that lists are expected
-// */
-//@Target(AnnotationTarget.PROPERTY)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class Multiple
-//
-///**
-// * Descriptor target
-// * The DataForge path to the resource containing the description. Following targets are supported:
-// *  1. resource
-// *  1. file
-// *  1. class
-// *  1. method
-// *  1. property
-// *
-// *
-// * Does not work if [type] is provided
-// */
-//@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY, AnnotationTarget.VALUE_PARAMETER)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class Descriptor(val value: String)
-//
-//
-///**
-// * Aggregator class for descriptor nodes
-// */
-//@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY, AnnotationTarget.FUNCTION, AnnotationTarget.VALUE_PARAMETER)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class DescriptorNodes(vararg val nodes: NodeDef)
-//
-///**
-// * Aggregator class for descriptor values
-// */
-//@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY, AnnotationTarget.FUNCTION, AnnotationTarget.VALUE_PARAMETER)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class DescriptorValues(vararg val nodes: ValueDef)
-//
-///**
-// * Alternative name for property descriptor declaration
-// */
-//@Target(AnnotationTarget.PROPERTY, AnnotationTarget.VALUE_PARAMETER)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class DescriptorName(val name: String)
-//
-//@Target(AnnotationTarget.PROPERTY)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class DescriptorValue(val def: ValueDef)
-////TODO enter fields directly?
-//
-//@Target(AnnotationTarget.PROPERTY)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class ValueProperty(
-//    val name: String = "",
-//    val type: Array<ValueType> = arrayOf(ValueType.STRING),
-//    val multiple: Boolean = false,
-//    val def: String = "",
-//    val enumeration: KClass<*> = Any::class,
-//    val tags: Array<String> = emptyArray()
-//)
-//
-//
-//@Target(AnnotationTarget.PROPERTY)
-//@Retention(AnnotationRetention.RUNTIME)
-//@MustBeDocumented
-//annotation class NodeProperty(val name: String = "")

dataforge-context/src/jvmMain/kotlin/space/kscience/dataforge/descriptors/reflectiveDescriptors.kt

@@ -1,53 +1,124 @@
 package space.kscience.dataforge.descriptors
 
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.decodeFromStream
+import org.slf4j.LoggerFactory
+import space.kscience.dataforge.meta.Scheme
+import space.kscience.dataforge.meta.SchemeSpec
+import space.kscience.dataforge.meta.ValueType
+import space.kscience.dataforge.meta.descriptors.MetaDescriptor
+import space.kscience.dataforge.meta.descriptors.MetaDescriptorBuilder
+import space.kscience.dataforge.meta.descriptors.node
+import java.net.URL
+import kotlin.reflect.KClass
+import kotlin.reflect.full.isSubclassOf
+import kotlin.reflect.full.memberProperties
+import kotlin.reflect.typeOf
 
-//inline fun <reified T : Scheme> T.buildDescriptor(): NodeDescriptor = NodeDescriptor {
-//    T::class.apply {
-//        findAnnotation<ItemDef>()?.let { def ->
-//            info = def.info
-//            required = def.required
-//            multiple = def.multiple
-//        }
-//        findAnnotation<Attribute>()?.let { attr ->
-//            attributes {
-//                this[attr.key] = attr.value.parseValue()
-//            }
-//        }
-//        findAnnotation<Attributes>()?.attrs?.forEach { attr ->
-//            attributes {
-//                this[attr.key] = attr.value.parseValue()
-//            }
-//        }
-//    }
-//    T::class.memberProperties.forEach { property ->
-//        val delegate = property.getDelegate(this@buildDescriptor)
-//
-//        val descriptor: ItemDescriptor = when (delegate) {
-//            is ConfigurableDelegate -> buildPropertyDescriptor(property, delegate)
-//            is ReadWriteDelegateWrapper<*, *> -> {
-//                if (delegate.delegate is ConfigurableDelegate) {
-//                    buildPropertyDescriptor(property, delegate.delegate as ConfigurableDelegate)
-//                } else {
-//                    return@forEach
-//                }
-//            }
-//            else -> return@forEach
-//        }
-//        defineItem(property.name, descriptor)
-//    }
-//}
 
-//inline fun <T : Scheme, reified V : Any?> buildPropertyDescriptor(
-//    property: KProperty1<T, V>,
-//    delegate: ConfigurableDelegate
-//): ItemDescriptor {
-//    when {
-//        V::class.isSubclassOf(Scheme::class) -> NodeDescriptor {
-//            default = delegate.default.node
-//        }
-//        V::class.isSubclassOf(Meta::class) -> NodeDescriptor {
-//            default = delegate.default.node
-//        }
-//
-//    }
-//}
+/**
+ * Description text for meta property, node or whole object
+ */
+@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
+@Retention(AnnotationRetention.RUNTIME)
+@MustBeDocumented
+public annotation class Description(val value: String)
+
+@Target(AnnotationTarget.PROPERTY)
+@Retention(AnnotationRetention.RUNTIME)
+@MustBeDocumented
+public annotation class Multiple()
+
+@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
+@Retention(AnnotationRetention.RUNTIME)
+@MustBeDocumented
+public annotation class DescriptorResource(val resourceName: String)
+
+@Target(AnnotationTarget.CLASS, AnnotationTarget.PROPERTY)
+@Retention(AnnotationRetention.RUNTIME)
+@MustBeDocumented
+public annotation class DescriptorUrl(val url: String)
+
+
+@OptIn(ExperimentalSerializationApi::class)
+private fun MetaDescriptorBuilder.loadDescriptorFromUrl(url: URL) {
+    url.openStream().use {
+        from(Json.decodeFromStream(MetaDescriptor.serializer(), it))
+    }
+}
+
+private fun MetaDescriptorBuilder.loadDescriptorFromResource(resource: DescriptorResource) {
+    val url = {}.javaClass.getResource(resource.resourceName)
+    if (url != null) {
+        loadDescriptorFromUrl(url)
+    } else {
+        LoggerFactory.getLogger("System")
+            .error("Can't find descriptor resource with name ${resource.resourceName}")
+    }
+}
+
+
+public fun <T : Any> MetaDescriptor.Companion.forClass(
+    kClass: KClass<T>,
+    mod: MetaDescriptorBuilder.() -> Unit = {},
+): MetaDescriptor = MetaDescriptor {
+    when {
+        kClass.isSubclassOf(Number::class) -> valueType(ValueType.NUMBER)
+        kClass == String::class -> ValueType.STRING
+        kClass == Boolean::class -> ValueType.BOOLEAN
+        kClass == DoubleArray::class -> ValueType.LIST
+    }
+
+    kClass.annotations.forEach {
+        when (it) {
+            is Description -> description = it.value
+
+            is DescriptorResource -> loadDescriptorFromResource(it)
+
+            is DescriptorUrl -> loadDescriptorFromUrl(URL(it.url))
+        }
+    }
+    kClass.memberProperties.forEach { property ->
+
+        var flag = false
+
+        val descriptor = MetaDescriptor {
+            //use base type descriptor as a base
+            (property.returnType.classifier as? KClass<*>)?.let {
+                from(forClass(it))
+            }
+            property.annotations.forEach {
+                when (it) {
+                    is Description -> {
+                        description = it.value
+                        flag = true
+                    }
+
+                    is Multiple -> {
+                        multiple = true
+                        flag = true
+                    }
+
+                    is DescriptorResource -> {
+                        loadDescriptorFromResource(it)
+                        flag = true
+                    }
+
+                    is DescriptorUrl -> {
+                        loadDescriptorFromUrl(URL(it.url))
+                        flag = true
+                    }
+                }
+            }
+        }
+        if (flag) {
+            node(property.name, descriptor)
+        }
+    }
+    mod()
+}
+
+@Suppress("UNCHECKED_CAST")
+public inline fun <reified T : Scheme> SchemeSpec<T>.autoDescriptor( noinline mod: MetaDescriptorBuilder.() -> Unit = {}): MetaDescriptor =
+    MetaDescriptor.forClass(typeOf<T>().classifier as KClass<T>, mod)

dataforge-context/src/jvmTest/kotlin/space/kscience/dataforge/descriptors/TestAutoDescriptors.kt

@@ -0,0 +1,31 @@
+package space.kscience.dataforge.descriptors
+
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import org.junit.jupiter.api.Test
+import space.kscience.dataforge.meta.Scheme
+import space.kscience.dataforge.meta.SchemeSpec
+import space.kscience.dataforge.meta.descriptors.MetaDescriptor
+import space.kscience.dataforge.meta.int
+import space.kscience.dataforge.meta.string
+
+private class TestScheme: Scheme(){
+
+    @Description("A")
+    val a by string()
+
+    @Description("B")
+    val b by int()
+
+    companion object: SchemeSpec<TestScheme>(::TestScheme){
+        override val descriptor: MetaDescriptor = autoDescriptor()
+    }
+}
+
+class TestAutoDescriptors {
+    @Test
+    fun autoDescriptor(){
+        val autoDescriptor = MetaDescriptor.forClass(TestScheme::class)
+        println(Json{prettyPrint = true}.encodeToString(autoDescriptor))
+    }
+}

dataforge-io/src/commonMain/kotlin/space/kscience/dataforge/io/Binary.kt

@@ -71,6 +71,11 @@ internal class ByteArrayBinary(
 
     override fun view(offset: Int, binarySize: Int): ByteArrayBinary =
         ByteArrayBinary(array, start + offset, binarySize)
+
+    override fun toString(): String =
+        "ByteArrayBinary(array=$array, start=$start, size=$size)"
+
+
 }
 
 public fun ByteArray.asBinary(): Binary = ByteArrayBinary(this)

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/JsonMeta.kt

@@ -31,7 +31,7 @@ private fun Meta.toJsonWithIndex(descriptor: MetaDescriptor?, index: String?): J
     val pairs: MutableList<Pair<String, JsonElement>> = items.entries.groupBy {
         it.key.body
     }.mapTo(ArrayList()) { (body, list) ->
-        val childDescriptor = descriptor?.children?.get(body)
+        val childDescriptor = descriptor?.nodes?.get(body)
         if (list.size == 1) {
             val (token, element) = list.first()
                 //do not add an empty element

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaConverter.kt

@@ -1,19 +1,19 @@
-package space.kscience.dataforge.meta.transformations
+package space.kscience.dataforge.meta
 
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.encodeToJsonElement
 import kotlinx.serialization.serializer
-import space.kscience.dataforge.meta.*
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
 import space.kscience.dataforge.misc.DFExperimental
 import kotlin.reflect.KType
 import kotlin.reflect.typeOf
 
+
 /**
  * A converter of generic object to and from [Meta]
  */
-public interface MetaConverter<T> {
+public interface MetaConverter<T>: MetaSpec<T> {
 
     /**
      * Runtime type of [T]
@@ -23,32 +23,32 @@ public interface MetaConverter<T> {
     /**
      * A descriptor for resulting meta
      */
-    public val descriptor: MetaDescriptor get() = MetaDescriptor.EMPTY
+    override val descriptor: MetaDescriptor get() = MetaDescriptor.EMPTY
 
     /**
-     * Attempt conversion of [meta] to an object or return null if conversion failed
+     * Attempt conversion of [source] to an object or return null if conversion failed
      */
-    public fun metaToObjectOrNull(meta: Meta): T?
+    override fun readOrNull(source: Meta): T?
 
-    public fun metaToObject(meta: Meta): T =
-        metaToObjectOrNull(meta) ?: error("Meta $meta could not be interpreted by $this")
+    override fun read(source: Meta): T =
+        readOrNull(source) ?: error("Meta $source could not be interpreted by $this")
 
-    public fun objectToMeta(obj: T): Meta
+    public fun convert(obj: T): Meta
 
     public companion object {
 
         public val meta: MetaConverter<Meta> = object : MetaConverter<Meta> {
             override val type: KType = typeOf<Meta>()
 
-            override fun metaToObjectOrNull(meta: Meta): Meta = meta
-            override fun objectToMeta(obj: Meta): Meta = obj
+            override fun readOrNull(source: Meta): Meta = source
+            override fun convert(obj: Meta): Meta = obj
         }
 
         public val value: MetaConverter<Value> = object : MetaConverter<Value> {
             override val type: KType = typeOf<Value>()
 
-            override fun metaToObjectOrNull(meta: Meta): Value? = meta.value
-            override fun objectToMeta(obj: Value): Meta = Meta(obj)
+            override fun readOrNull(source: Meta): Value? = source.value
+            override fun convert(obj: Value): Meta = Meta(obj)
         }
 
         public val string: MetaConverter<String> = object : MetaConverter<String> {
@@ -59,8 +59,8 @@ public interface MetaConverter<T> {
             }
 
 
-            override fun metaToObjectOrNull(meta: Meta): String? = meta.string
-            override fun objectToMeta(obj: String): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): String? = source.string
+            override fun convert(obj: String): Meta = Meta(obj.asValue())
         }
 
         public val boolean: MetaConverter<Boolean> = object : MetaConverter<Boolean> {
@@ -70,8 +70,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.BOOLEAN)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Boolean? = meta.boolean
-            override fun objectToMeta(obj: Boolean): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Boolean? = source.boolean
+            override fun convert(obj: Boolean): Meta = Meta(obj.asValue())
         }
 
         public val number: MetaConverter<Number> = object : MetaConverter<Number> {
@@ -81,8 +81,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.NUMBER)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Number? = meta.number
-            override fun objectToMeta(obj: Number): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Number? = source.number
+            override fun convert(obj: Number): Meta = Meta(obj.asValue())
         }
 
         public val double: MetaConverter<Double> = object : MetaConverter<Double> {
@@ -92,8 +92,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.NUMBER)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Double? = meta.double
-            override fun objectToMeta(obj: Double): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Double? = source.double
+            override fun convert(obj: Double): Meta = Meta(obj.asValue())
         }
 
         public val float: MetaConverter<Float> = object : MetaConverter<Float> {
@@ -103,8 +103,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.NUMBER)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Float? = meta.float
-            override fun objectToMeta(obj: Float): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Float? = source.float
+            override fun convert(obj: Float): Meta = Meta(obj.asValue())
         }
 
         public val int: MetaConverter<Int> = object : MetaConverter<Int> {
@@ -114,8 +114,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.NUMBER)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Int? = meta.int
-            override fun objectToMeta(obj: Int): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Int? = source.int
+            override fun convert(obj: Int): Meta = Meta(obj.asValue())
         }
 
         public val long: MetaConverter<Long> = object : MetaConverter<Long> {
@@ -125,8 +125,8 @@ public interface MetaConverter<T> {
                 valueType(ValueType.NUMBER)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): Long? = meta.long
-            override fun objectToMeta(obj: Long): Meta = Meta(obj.asValue())
+            override fun readOrNull(source: Meta): Long? = source.long
+            override fun convert(obj: Long): Meta = Meta(obj.asValue())
         }
 
         public inline fun <reified E : Enum<E>> enum(): MetaConverter<E> = object : MetaConverter<E> {
@@ -138,9 +138,9 @@ public interface MetaConverter<T> {
             }
 
             @Suppress("USELESS_CAST")
-            override fun metaToObjectOrNull(meta: Meta): E = meta.enum<E>() as? E ?: error("The Item is not a Enum")
+            override fun readOrNull(source: Meta): E = source.enum<E>() as? E ?: error("The Item is not a Enum")
 
-            override fun objectToMeta(obj: E): Meta = Meta(obj.asValue())
+            override fun convert(obj: E): Meta = Meta(obj.asValue())
         }
 
         public fun <T> valueList(
@@ -153,9 +153,9 @@ public interface MetaConverter<T> {
                 valueType(ValueType.LIST)
             }
 
-            override fun metaToObjectOrNull(meta: Meta): List<T>? = meta.value?.list?.map(reader)
+            override fun readOrNull(source: Meta): List<T>? = source.value?.list?.map(reader)
 
-            override fun objectToMeta(obj: List<T>): Meta = Meta(obj.map(writer).asValue())
+            override fun convert(obj: List<T>): Meta = Meta(obj.map(writer).asValue())
         }
 
         /**
@@ -168,12 +168,12 @@ public interface MetaConverter<T> {
             override val type: KType = typeOf<T>()
             private val serializer: KSerializer<T> = serializer()
 
-            override fun metaToObjectOrNull(meta: Meta): T? {
-                val json = meta.toJson(descriptor)
+            override fun readOrNull(source: Meta): T? {
+                val json = source.toJson(descriptor)
                 return Json.decodeFromJsonElement(serializer, json)
             }
 
-            override fun objectToMeta(obj: T): Meta {
+            override fun convert(obj: T): Meta {
                 val json = Json.encodeToJsonElement(obj)
                 return json.toMeta(descriptor)
             }
@@ -183,7 +183,6 @@ public interface MetaConverter<T> {
     }
 }
 
-public fun <T : Any> MetaConverter<T>.nullableMetaToObject(item: Meta?): T? = item?.let { metaToObject(it) }
-public fun <T : Any> MetaConverter<T>.nullableObjectToMeta(obj: T?): Meta? = obj?.let { objectToMeta(it) }
+public fun <T : Any> MetaConverter<T>.convertNullable(obj: T?): Meta? = obj?.let { convert(it) }
+
 
-public fun <T> MetaConverter<T>.valueToObject(value: Value): T? = metaToObject(Meta(value))

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaDelegate.kt

@@ -1,7 +1,6 @@
 package space.kscience.dataforge.meta
 
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
-import space.kscience.dataforge.meta.transformations.MetaConverter
 import space.kscience.dataforge.misc.DFExperimental
 import space.kscience.dataforge.names.Name
 import space.kscience.dataforge.names.asName
@@ -14,13 +13,13 @@ public fun MetaProvider.node(key: Name? = null): ReadOnlyProperty<Any?, Meta?> =
 }
 
 /**
- * Use [converter] to read the Meta node
+ * Use [metaSpec] to read the Meta node
  */
-public fun <T> MetaProvider.convertable(
-    converter: MetaConverter<T>,
+public fun <T> MetaProvider.spec(
+    metaSpec: MetaSpec<T>,
     key: Name? = null,
 ): ReadOnlyProperty<Any?, T?> = ReadOnlyProperty { _, property ->
-    get(key ?: property.name.asName())?.let { converter.metaToObject(it) }
+    get(key ?: property.name.asName())?.let { metaSpec.read(it) }
 }
 
 /**
@@ -30,30 +29,30 @@ public fun <T> MetaProvider.convertable(
 public inline fun <reified T> MetaProvider.serializable(
     descriptor: MetaDescriptor? = null,
     key: Name? = null,
-): ReadOnlyProperty<Any?, T?> = convertable(MetaConverter.serializable(descriptor), key)
+): ReadOnlyProperty<Any?, T?> = spec(MetaConverter.serializable(descriptor), key)
 
 @Deprecated("Use convertable", ReplaceWith("convertable(converter, key)"))
 public fun <T> MetaProvider.node(
     key: Name? = null,
-    converter: MetaConverter<T>,
-): ReadOnlyProperty<Any?, T?> = convertable(converter, key)
+    converter: MetaSpec<T>,
+): ReadOnlyProperty<Any?, T?> = spec(converter, key)
 
 /**
  * Use [converter] to convert a list of same name siblings meta to object
  */
-public fun <T> Meta.listOfConvertable(
-    converter: MetaConverter<T>,
+public fun <T> Meta.listOfSpec(
+    converter: MetaSpec<T>,
     key: Name? = null,
 ): ReadOnlyProperty<Any?, List<T>> = ReadOnlyProperty{_, property ->
     val name = key ?: property.name.asName()
-    getIndexed(name).values.map { converter.metaToObject(it) }
+    getIndexed(name).values.map { converter.read(it) }
 }
 
 @DFExperimental
 public inline fun <reified T> Meta.listOfSerializable(
     descriptor: MetaDescriptor? = null,
     key: Name? = null,
-): ReadOnlyProperty<Any?, List<T>> = listOfConvertable(MetaConverter.serializable(descriptor), key)
+): ReadOnlyProperty<Any?, List<T>> = listOfSpec(MetaConverter.serializable(descriptor), key)
 
 /**
  * A property delegate that uses custom key

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaSpec.kt

@@ -0,0 +1,21 @@
+package space.kscience.dataforge.meta
+
+import space.kscience.dataforge.meta.descriptors.Described
+
+public interface MetaSpec<out T> : Described {
+
+    /**
+     * Read the source meta into an object and return null if Meta could not be interpreted as a target type
+     */
+    public fun readOrNull(source: Meta): T?
+
+    /**
+     * Read generic read-only meta with this [MetaSpec] producing instance of the desired type.
+     * Throws an error if conversion could not be done.
+     */
+    public fun read(source: Meta): T = readOrNull(source) ?: error("Meta $source could not be interpreted by $this")
+}
+
+
+public fun <T : Any> MetaSpec<T>.readNullable(item: Meta?): T? = item?.let { read(it) }
+public fun <T> MetaSpec<T>.readValue(value: Value): T? = read(Meta(value))

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MetaTransformation.kt

@@ -1,6 +1,5 @@
-package space.kscience.dataforge.meta.transformations
+package space.kscience.dataforge.meta
 
-import space.kscience.dataforge.meta.*
 import space.kscience.dataforge.misc.DFExperimental
 import space.kscience.dataforge.names.Name
 import kotlin.jvm.JvmInline

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/MutableMetaDelegate.kt

@@ -1,7 +1,6 @@
 package space.kscience.dataforge.meta
 
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
-import space.kscience.dataforge.meta.transformations.MetaConverter
 import space.kscience.dataforge.misc.DFExperimental
 import space.kscience.dataforge.names.Name
 import space.kscience.dataforge.names.asName
@@ -33,12 +32,12 @@ public fun <T> MutableMetaProvider.convertable(
     object : ReadWriteProperty<Any?, T?> {
         override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
             val name = key ?: property.name.asName()
-            return get(name)?.let { converter.metaToObject(it) }
+            return get(name)?.let { converter.read(it) }
         }
 
         override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
             val name = key ?: property.name.asName()
-            set(name, value?.let { converter.objectToMeta(it) })
+            set(name, value?.let { converter.convert(it) })
         }
     }
 
@@ -66,12 +65,12 @@ public fun <T> MutableMeta.listOfConvertable(
 ): ReadWriteProperty<Any?, List<T>> = object : ReadWriteProperty<Any?, List<T>> {
     override fun getValue(thisRef: Any?, property: KProperty<*>): List<T> {
         val name = key ?: property.name.asName()
-        return getIndexed(name).values.map { converter.metaToObject(it) }
+        return getIndexed(name).values.map { converter.read(it) }
     }
 
     override fun setValue(thisRef: Any?, property: KProperty<*>, value: List<T>) {
         val name = key ?: property.name.asName()
-        setIndexed(name, value.map { converter.objectToMeta(it) })
+        setIndexed(name, value.map { converter.convert(it) })
     }
 }
 

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/ObservableMeta.kt

@@ -1,8 +1,10 @@
 package space.kscience.dataforge.meta
 
 import space.kscience.dataforge.misc.ThreadSafe
-import space.kscience.dataforge.names.*
-import kotlin.reflect.KProperty1
+import space.kscience.dataforge.names.Name
+import space.kscience.dataforge.names.cutFirst
+import space.kscience.dataforge.names.firstOrNull
+import space.kscience.dataforge.names.isEmpty
 
 
 internal data class MetaListener(
@@ -15,12 +17,15 @@ internal data class MetaListener(
  */
 public interface ObservableMeta : Meta {
     /**
-     * Add change listener to this meta. Owner is declared to be able to remove listeners later. Listener without owner could not be removed
+     * Add change listener to this meta. The Owner is declared to be able to remove listeners later.
+     * Listeners without an owner could be only removed all together.
+     *
+     * `this` object in the listener represents the current state of this meta. The name points to a changed node
      */
     public fun onChange(owner: Any?, callback: Meta.(name: Name) -> Unit)
 
     /**
-     * Remove all listeners belonging to given owner
+     * Remove all listeners belonging to the given [owner]. Passing null removes all listeners.
      */
     public fun removeListener(owner: Any?)
 
@@ -67,24 +72,4 @@ internal abstract class AbstractObservableMeta : ObservableMeta {
     override fun toString(): String = Meta.toString(this)
     override fun equals(other: Any?): Boolean = Meta.equals(this, other as? Meta)
     override fun hashCode(): Int = Meta.hashCode(this)
-}
-
-/**
- * Use the value of the property in a [callBack].
- * The callback is called once immediately after subscription to pass the initial value.
- *
- * Optional [owner] property is used for
- */
-public fun <S : Scheme, T> S.useProperty(
-    property: KProperty1<S, T>,
-    owner: Any? = null,
-    callBack: S.(T) -> Unit,
-) {
-    //Pass initial value.
-    callBack(property.get(this))
-    meta.onChange(owner) { name ->
-        if (name.startsWith(property.name.asName())) {
-            callBack(property.get(this@useProperty))
-        }
-    }
 }

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Scheme.kt

@@ -7,36 +7,49 @@ import space.kscience.dataforge.meta.descriptors.validate
 import space.kscience.dataforge.misc.DFExperimental
 import space.kscience.dataforge.misc.ThreadSafe
 import space.kscience.dataforge.names.*
+import kotlin.properties.ReadWriteProperty
+import kotlin.reflect.KProperty
+import kotlin.reflect.KProperty1
 
 /**
- * A base for delegate-based or descriptor-based scheme. [Scheme] has an empty constructor to simplify usage from [Specification].
+ * A base for delegate-based or descriptor-based scheme. [Scheme] has an empty constructor to simplify usage from [MetaSpec].
  * Default item provider and [MetaDescriptor] are optional
  */
 public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurable {
 
     /**
-     * Meta to be mutated by this schme
+     * Meta to be mutated by this scheme
      */
-    private var targetMeta: MutableMeta = MutableMeta()
+    private var target: MutableMeta? = null
+        get() {
+            // automatic initialization of target if it is missing
+            if (field == null) {
+                field = MutableMeta()
+            }
+            return field
+        }
 
     /**
      * Default values provided by this scheme
      */
-    private var defaultMeta: Meta? = null
+    private var prototype: Meta? = null
 
     final override val meta: ObservableMutableMeta = SchemeMeta(Name.EMPTY)
 
     final override var descriptor: MetaDescriptor? = null
-        internal set
+        private set
 
-    internal fun wrap(
-        newMeta: MutableMeta,
-        preserveDefault: Boolean = false,
+    /**
+     * This method must be called before the scheme could be used
+     */
+    internal fun initialize(
+        target: MutableMeta,
+        prototype: Meta,
+        descriptor: MetaDescriptor?,
     ) {
-        if (preserveDefault) {
-            defaultMeta = targetMeta.seal()
-        }
-        targetMeta = newMeta
+        this.target = target
+        this.prototype = prototype
+        this.descriptor = descriptor
     }
 
     /**
@@ -47,11 +60,11 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
         return descriptor?.validate(meta) ?: true
     }
 
-    override fun get(name: Name): MutableMeta? = meta.get(name)
+    override fun get(name: Name): MutableMeta? = meta[name]
 
     override fun set(name: Name, node: Meta?) {
         if (validate(name, meta)) {
-            meta.set(name, node)
+            meta[name] = node
         } else {
             error("Validation failed for node $node at $name")
         }
@@ -68,14 +81,16 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
 
     private val listeners: MutableList<MetaListener> = mutableListOf()
 
+    override fun toString(): String = meta.toString()
+
     private inner class SchemeMeta(val pathName: Name) : ObservableMutableMeta {
         override var value: Value?
-            get() = targetMeta[pathName]?.value
-                ?: defaultMeta?.get(pathName)?.value
+            get() = target[pathName]?.value
+                ?: prototype?.get(pathName)?.value
                 ?: descriptor?.get(pathName)?.defaultValue
             set(value) {
-                val oldValue = targetMeta[pathName]?.value
-                targetMeta[pathName] = value
+                val oldValue = target[pathName]?.value
+                target!![pathName] = value
                 if (oldValue != value) {
                     invalidate(Name.EMPTY)
                 }
@@ -83,8 +98,8 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
 
         override val items: Map<NameToken, ObservableMutableMeta>
             get() {
-                val targetKeys = targetMeta[pathName]?.items?.keys ?: emptySet()
-                val defaultKeys = defaultMeta?.get(pathName)?.items?.keys ?: emptySet()
+                val targetKeys = target[pathName]?.items?.keys ?: emptySet()
+                val defaultKeys = prototype?.get(pathName)?.items?.keys ?: emptySet()
                 return (targetKeys + defaultKeys).associateWith { SchemeMeta(pathName + it) }
             }
 
@@ -111,7 +126,7 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
         override fun hashCode(): Int = Meta.hashCode(this)
 
         override fun set(name: Name, node: Meta?) {
-            targetMeta.set(name, node)
+            target!![name] = node
             invalidate(name)
         }
 
@@ -119,7 +134,6 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
 
         @DFExperimental
         override fun attach(name: Name, node: ObservableMutableMeta) {
-            //TODO implement zero-copy attachment
             set(name, node)
             node.onChange(this) { changeName ->
                 set(name + changeName, this[changeName])
@@ -131,10 +145,11 @@ public open class Scheme : Described, MetaRepr, MutableMetaProvider, Configurabl
 
 /**
  * Relocate scheme target onto given [MutableMeta]. Old provider does not get updates anymore.
- * Current state of the scheme used as a default.
+ * The Current state of the scheme that os used as a default.
  */
+@DFExperimental
 public fun <T : Scheme> T.retarget(provider: MutableMeta): T = apply {
-    wrap(provider, true)
+    initialize(provider, meta.seal(), descriptor)
 }
 
 /**
@@ -153,24 +168,145 @@ public inline fun <T : Scheme> T.copy(spec: SchemeSpec<T>, block: T.() -> Unit =
  */
 public open class SchemeSpec<out T : Scheme>(
     private val builder: () -> T,
-) : Specification<T> {
+) : MetaSpec<T> {
 
-    override fun read(source: Meta): T = builder().also {
-        it.wrap(MutableMeta().withDefault(source))
-    }
-
-    override fun write(target: MutableMeta): T = empty().also {
-        it.wrap(target)
-    }
-
-    //TODO Generate descriptor from Scheme class
     override val descriptor: MetaDescriptor? get() = null
 
-    override fun empty(): T = builder().also {
-        it.descriptor = descriptor
+    override fun readOrNull(source: Meta): T = builder().also {
+        it.initialize(MutableMeta(), source, descriptor)
     }
 
-    @Suppress("OVERRIDE_BY_INLINE")
-    final override inline operator fun invoke(action: T.() -> Unit): T = empty().apply(action)
+    public fun write(target: MutableMeta): T = empty().also {
+        it.initialize(target, Meta.EMPTY, descriptor)
+    }
 
+    /**
+     * Generate an empty object
+     */
+    public fun empty(): T = builder().also {
+        it.initialize(MutableMeta(), Meta.EMPTY, descriptor)
+    }
+
+    /**
+     * A convenience method to use specifications in builders
+     */
+    public inline operator fun invoke(action: T.() -> Unit): T = empty().apply(action)
+
+}
+
+
+
+/**
+ * Update a [MutableMeta] using given specification
+ */
+public fun <T : Scheme> MutableMeta.updateWith(
+    spec: SchemeSpec<T>,
+    action: T.() -> Unit,
+): T = spec.write(this).apply(action)
+
+
+/**
+ * Update configuration using given specification
+ */
+public fun <T : Scheme> Configurable.updateWith(
+    spec: SchemeSpec<T>,
+    action: T.() -> Unit,
+): T = spec.write(meta).apply(action)
+
+
+/**
+ * A delegate that uses a [MetaSpec] to wrap a child of this provider
+ */
+public fun <T : Scheme> MutableMeta.scheme(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, T> = object : ReadWriteProperty<Any?, T> {
+    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
+        val name = key ?: property.name.asName()
+        return spec.write(getOrCreate(name))
+    }
+
+    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
+        val name = key ?: property.name.asName()
+        set(name, value.toMeta())
+    }
+}
+
+public fun <T : Scheme> Scheme.scheme(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, T> = meta.scheme(spec, key)
+
+/**
+ * A delegate that uses a [MetaSpec] to wrap a child of this provider.
+ * Returns null if meta with given name does not exist.
+ */
+public fun <T : Scheme> MutableMeta.schemeOrNull(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, T?> = object : ReadWriteProperty<Any?, T?> {
+    override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
+        val name = key ?: property.name.asName()
+        return if (get(name) == null) null else spec.write(getOrCreate(name))
+    }
+
+    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
+        val name = key ?: property.name.asName()
+        if (value == null) remove(name)
+        else set(name, value.toMeta())
+    }
+}
+
+public fun <T : Scheme> Scheme.schemeOrNull(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, T?> = meta.schemeOrNull(spec, key)
+
+/**
+ * A delegate that uses a [MetaSpec] to wrap a list of child providers.
+ * If children are mutable, the changes in list elements are reflected on them.
+ * The list is a snapshot of children state, so change in structure is not reflected on its composition.
+ */
+@DFExperimental
+public fun <T : Scheme> MutableMeta.listOfScheme(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, List<T>> = object : ReadWriteProperty<Any?, List<T>> {
+    override fun getValue(thisRef: Any?, property: KProperty<*>): List<T> {
+        val name = key ?: property.name.asName()
+        return getIndexed(name).values.map { spec.write(it as MutableMeta) }
+    }
+
+    override fun setValue(thisRef: Any?, property: KProperty<*>, value: List<T>) {
+        val name = key ?: property.name.asName()
+        setIndexed(name, value.map { it.toMeta() })
+    }
+}
+
+
+@DFExperimental
+public fun <T : Scheme> Scheme.listOfScheme(
+    spec: SchemeSpec<T>,
+    key: Name? = null,
+): ReadWriteProperty<Any?, List<T>> = meta.listOfScheme(spec, key)
+
+
+/**
+ * Use the value of the property in a [callBack].
+ * The callback is called once immediately after subscription to pass the initial value.
+ *
+ * Optional [owner] property is used for
+ */
+public fun <S : Scheme, T> S.useProperty(
+    property: KProperty1<S, T>,
+    owner: Any? = null,
+    callBack: S.(T) -> Unit,
+) {
+    //Pass initial value.
+    callBack(property.get(this))
+    meta.onChange(owner) { name ->
+        if (name.startsWith(property.name.asName())) {
+            callBack(property.get(this@useProperty))
+        }
+    }
 }

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/Specification.kt

@@ -1,137 +0,0 @@
-package space.kscience.dataforge.meta
-
-import space.kscience.dataforge.meta.descriptors.Described
-import space.kscience.dataforge.misc.DFExperimental
-import space.kscience.dataforge.names.Name
-import space.kscience.dataforge.names.asName
-import kotlin.properties.ReadWriteProperty
-import kotlin.reflect.KProperty
-
-public interface ReadOnlySpecification<out T : Any> : Described {
-
-    /**
-     * Read generic read-only meta with this [Specification] producing instance of desired type.
-     * The source is not mutated even if it is in theory mutable
-     */
-    public fun read(source: Meta): T
-
-    /**
-     * Generate an empty object
-     */
-    public fun empty(): T
-
-    /**
-     * A convenience method to use specifications in builders
-     */
-    public operator fun invoke(action: T.() -> Unit): T = empty().apply(action)
-}
-
-
-/**
- * Allows to apply custom configuration in a type safe way to simple untyped configuration.
- * By convention [Scheme] companion should inherit this class
- *
- */
-public interface Specification<out T : Any> : ReadOnlySpecification<T> {
-    /**
-     * Wrap [MutableMeta], using it as inner storage (changes to [Specification] are reflected on [MutableMeta]
-     */
-    public fun write(target: MutableMeta): T
-}
-
-/**
- * Update a [MutableMeta] using given specification
- */
-public fun <T : Any> MutableMeta.updateWith(
-    spec: Specification<T>,
-    action: T.() -> Unit,
-): T = spec.write(this).apply(action)
-
-
-/**
- * Update configuration using given specification
- */
-public fun <T : Any> Configurable.updateWith(
-    spec: Specification<T>,
-    action: T.() -> Unit,
-): T = spec.write(meta).apply(action)
-
-//
-//public fun  <M : MutableTypedMeta<M>> MutableMeta.withSpec(spec: Specification<M>): M? =
-//    spec.write(it)
-
-/**
- * A delegate that uses a [Specification] to wrap a child of this provider
- */
-public fun <T : Scheme> MutableMeta.spec(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, T> = object : ReadWriteProperty<Any?, T> {
-    override fun getValue(thisRef: Any?, property: KProperty<*>): T {
-        val name = key ?: property.name.asName()
-        return spec.write(getOrCreate(name))
-    }
-
-    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
-        val name = key ?: property.name.asName()
-        set(name, value.toMeta())
-    }
-}
-
-public fun <T : Scheme> Scheme.spec(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, T> = meta.spec(spec, key)
-
-/**
- * A delegate that uses a [Specification] to wrap a child of this provider.
- * Returns null if meta with given name does not exist.
- */
-public fun <T : Scheme> MutableMeta.specOrNull(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, T?> = object : ReadWriteProperty<Any?, T?> {
-    override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
-        val name = key ?: property.name.asName()
-        return if (get(name) == null) null else spec.write(getOrCreate(name))
-    }
-
-    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
-        val name = key ?: property.name.asName()
-        if (value == null) remove(name)
-        else set(name, value.toMeta())
-    }
-}
-
-public fun <T : Scheme> Scheme.specOrNull(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, T?> = meta.specOrNull(spec, key)
-
-/**
- * A delegate that uses a [Specification] to wrap a list of child providers.
- * If children are mutable, the changes in list elements are reflected on them.
- * The list is a snapshot of children state, so change in structure is not reflected on its composition.
- */
-@DFExperimental
-public fun <T : Scheme> MutableMeta.listOfSpec(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, List<T>> = object : ReadWriteProperty<Any?, List<T>> {
-    override fun getValue(thisRef: Any?, property: KProperty<*>): List<T> {
-        val name = key ?: property.name.asName()
-        return getIndexed(name).values.map { spec.write(it as MutableMeta) }
-    }
-
-    override fun setValue(thisRef: Any?, property: KProperty<*>, value: List<T>) {
-        val name = key ?: property.name.asName()
-        setIndexed(name, value.map { it.toMeta() })
-    }
-}
-
-
-@DFExperimental
-public fun <T : Scheme> Scheme.listOfSpec(
-    spec: Specification<T>,
-    key: Name? = null,
-): ReadWriteProperty<Any?, List<T>> = meta.listOfSpec(spec, key)

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/descriptors/MetaDescriptor.kt

@@ -27,7 +27,7 @@ public enum class ValueRestriction {
 /**
  * The descriptor for a meta
  * @param description description text
- * @param children child descriptors for this node
+ * @param nodes child descriptors for this node
  * @param multiple True if same name siblings with this name are allowed
  * @param valueRestriction The requirements for node content
  * @param valueTypes list of allowed types for [Meta.value], null if all values are allowed.
@@ -39,7 +39,7 @@ public enum class ValueRestriction {
 @Serializable
 public data class MetaDescriptor(
     public val description: String? = null,
-    public val children: Map<String, MetaDescriptor> = emptyMap(),
+    public val nodes: Map<String, MetaDescriptor> = emptyMap(),
     public val multiple: Boolean = false,
     public val valueRestriction: ValueRestriction = ValueRestriction.NONE,
     public val valueTypes: List<ValueType>? = null,
@@ -47,6 +47,9 @@ public data class MetaDescriptor(
     public val defaultValue: Value? = null,
     public val attributes: Meta = Meta.EMPTY,
 ) {
+    @Deprecated("Replace by nodes", ReplaceWith("nodes"))
+    public val children: Map<String, MetaDescriptor> get() = nodes
+
     /**
      * A node constructed of default values for this descriptor and its children
      */
@@ -55,7 +58,7 @@ public data class MetaDescriptor(
             defaultValue?.let { defaultValue ->
                 this.value = defaultValue
             }
-            children.forEach { (key, descriptor) ->
+            nodes.forEach { (key, descriptor) ->
                 set(key, descriptor.defaultNode)
             }
         }
@@ -67,13 +70,13 @@ public data class MetaDescriptor(
     }
 }
 
-public val MetaDescriptor.required: Boolean get() = valueRestriction == ValueRestriction.REQUIRED || children.values.any { required }
+public val MetaDescriptor.required: Boolean get() = valueRestriction == ValueRestriction.REQUIRED || nodes.values.any { required }
 
 public val MetaDescriptor.allowedValues: List<Value>? get() = attributes[MetaDescriptor.ALLOWED_VALUES_KEY]?.value?.list
 
 public operator fun MetaDescriptor.get(name: Name): MetaDescriptor? = when (name.length) {
     0 -> this
-    1 -> children[name.firstOrNull()!!.toString()]
+    1 -> nodes[name.firstOrNull()!!.toString()]
     else -> get(name.firstOrNull()!!.asName())?.get(name.cutFirst())
 }
 
@@ -95,7 +98,7 @@ public fun MetaDescriptor.validate(item: Meta?): Boolean {
     if (item == null) return !required
     if (!validate(item.value)) return false
 
-    children.forEach { (key, childDescriptor) ->
+    nodes.forEach { (key, childDescriptor) ->
         if (!childDescriptor.validate(item[key])) return false
     }
     return true

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/descriptors/MetaDescriptorBuilder.kt

@@ -44,38 +44,27 @@ public class MetaDescriptorBuilder @PublishedApi internal constructor() {
         attributes.apply(block)
     }
 
-    public fun item(name: Name, block: MetaDescriptorBuilder.() -> Unit = {}): MetaDescriptorBuilder {
-        return when (name.length) {
-            0 -> apply(block)
+    internal fun node(
+        name: Name,
+        descriptorBuilder: MetaDescriptorBuilder,
+    ): Unit {
+        when (name.length) {
+            0 -> error("Can't set descriptor to root")
             1 -> {
-                val target = MetaDescriptorBuilder().apply(block)
-                children[name.first().body] = target
-                target
+                children[name.first().body] = descriptorBuilder
             }
 
-            else -> {
-                children.getOrPut(name.first().body) { MetaDescriptorBuilder() }.item(name.cutFirst(), block)
-            }
+            else -> children.getOrPut(name.first().body) {
+                MetaDescriptorBuilder()
+            }.node(name.cutFirst(), descriptorBuilder)
         }
     }
 
-    public fun node(
+    internal fun node(
         name: Name,
-        descriptor: MetaDescriptor,
-        block: MetaDescriptorBuilder.() -> Unit = {},
-    ): MetaDescriptorBuilder = when (name.length) {
-        0 -> error("Can't set descriptor to root")
-        1 -> {
-            val item = descriptor.toBuilder().apply {
-                valueRestriction = ValueRestriction.ABSENT
-            }.apply(block)
-            children[name.first().body] = item
-            item
-        }
-
-        else -> children.getOrPut(name.first().body) {
-            MetaDescriptorBuilder()
-        }.node(name.cutFirst(), descriptor, block)
+        descriptorBuilder: MetaDescriptor,
+    ): Unit {
+        node(name, descriptorBuilder.toBuilder())
     }
 
     public var allowedValues: List<Value>
@@ -89,10 +78,21 @@ public class MetaDescriptorBuilder @PublishedApi internal constructor() {
         allowedValues = values.map { Value.of(it) }
     }
 
+    public fun from(descriptor: MetaDescriptor) {
+        description = descriptor.description
+        children.putAll(descriptor.nodes.mapValues { it.value.toBuilder() })
+        multiple = descriptor.multiple
+        valueRestriction = descriptor.valueRestriction
+        valueTypes = descriptor.valueTypes
+        indexKey = descriptor.indexKey
+        default = descriptor.defaultValue
+        attributes.update(descriptor.attributes)
+    }
+
     @PublishedApi
     internal fun build(): MetaDescriptor = MetaDescriptor(
         description = description,
-        children = children.mapValues { it.value.build() },
+        nodes = children.mapValues { it.value.build() },
         multiple = multiple,
         valueRestriction = valueRestriction,
         valueTypes = valueTypes,
@@ -102,12 +102,57 @@ public class MetaDescriptorBuilder @PublishedApi internal constructor() {
     )
 }
 
-public fun MetaDescriptorBuilder.item(name: String, block: MetaDescriptorBuilder.() -> Unit): MetaDescriptorBuilder =
-    item(Name.parse(name), block)
+//public fun MetaDescriptorBuilder.item(name: String, block: MetaDescriptorBuilder.() -> Unit): MetaDescriptorBuilder =
+//    item(Name.parse(name), block)
 
 public inline fun MetaDescriptor(block: MetaDescriptorBuilder.() -> Unit): MetaDescriptor =
     MetaDescriptorBuilder().apply(block).build()
 
+/**
+ * Create and configure child node descriptor
+ */
+public fun MetaDescriptorBuilder.node(
+    name: Name,
+    block: MetaDescriptorBuilder.() -> Unit,
+) {
+    node(
+        name,
+        MetaDescriptorBuilder().apply(block)
+    )
+}
+
+public fun MetaDescriptorBuilder.node(name: String, descriptor: MetaDescriptor) {
+    node(Name.parse(name), descriptor)
+}
+
+public fun MetaDescriptorBuilder.node(name: String, block: MetaDescriptorBuilder.() -> Unit) {
+    node(Name.parse(name), block)
+}
+
+public fun MetaDescriptorBuilder.node(
+    key: String,
+    base: Described,
+    block: MetaDescriptorBuilder.() -> Unit = {},
+) {
+    node(Name.parse(key), base.descriptor?.toBuilder()?.apply(block) ?: MetaDescriptorBuilder())
+}
+
+public fun MetaDescriptorBuilder.required() {
+    valueRestriction = ValueRestriction.REQUIRED
+}
+
+private fun MetaDescriptor.toBuilder(): MetaDescriptorBuilder = MetaDescriptorBuilder().apply {
+    description = this@toBuilder.description
+    children = this@toBuilder.nodes.mapValuesTo(LinkedHashMap()) { it.value.toBuilder() }
+    multiple = this@toBuilder.multiple
+    valueRestriction = this@toBuilder.valueRestriction
+    valueTypes = this@toBuilder.valueTypes
+    indexKey = this@toBuilder.indexKey
+    default = defaultValue
+    attributes = this@toBuilder.attributes.toMutableMeta()
+}
+
+
 /**
  * Create and configure child value descriptor
  */
@@ -116,7 +161,7 @@ public fun MetaDescriptorBuilder.value(
     type: ValueType,
     vararg additionalTypes: ValueType,
     block: MetaDescriptorBuilder.() -> Unit = {},
-): MetaDescriptorBuilder = item(name) {
+): Unit = node(name) {
     valueType(type, *additionalTypes)
     block()
 }
@@ -126,41 +171,14 @@ public fun MetaDescriptorBuilder.value(
     type: ValueType,
     vararg additionalTypes: ValueType,
     block: MetaDescriptorBuilder.() -> Unit = {},
-): MetaDescriptorBuilder = value(Name.parse(name), type, additionalTypes = additionalTypes, block)
+): Unit = value(Name.parse(name), type, additionalTypes = additionalTypes, block)
 
-/**
- * Create and configure child value descriptor
- */
-public fun MetaDescriptorBuilder.node(
-    name: Name, block: MetaDescriptorBuilder.() -> Unit,
-): MetaDescriptorBuilder = item(name) {
-    valueRestriction = ValueRestriction.ABSENT
-    block()
-}
-
-public fun MetaDescriptorBuilder.node(name: String, block: MetaDescriptorBuilder.() -> Unit) {
-    node(Name.parse(name), block)
-}
-
-public fun MetaDescriptorBuilder.node(
-    key: String,
-    described: Described,
-    block: MetaDescriptorBuilder.() -> Unit = {},
-) {
-    described.descriptor?.let {
-        node(Name.parse(key), it, block)
-    }
-}
-
-public fun MetaDescriptorBuilder.required() {
-    valueRestriction = ValueRestriction.REQUIRED
-}
 
 public inline fun <reified E : Enum<E>> MetaDescriptorBuilder.enum(
     key: Name,
     default: E?,
     crossinline modifier: MetaDescriptorBuilder.() -> Unit = {},
-): MetaDescriptorBuilder = value(key, ValueType.STRING) {
+): Unit = value(key, ValueType.STRING) {
     default?.let {
         this.default = default.asValue()
     }
@@ -168,17 +186,6 @@ public inline fun <reified E : Enum<E>> MetaDescriptorBuilder.enum(
     modifier()
 }
 
-private fun MetaDescriptor.toBuilder(): MetaDescriptorBuilder = MetaDescriptorBuilder().apply {
-    description = this@toBuilder.description
-    children = this@toBuilder.children.mapValuesTo(LinkedHashMap()) { it.value.toBuilder() }
-    multiple = this@toBuilder.multiple
-    valueRestriction = this@toBuilder.valueRestriction
-    valueTypes = this@toBuilder.valueTypes
-    indexKey = this@toBuilder.indexKey
-    default = defaultValue
-    attributes = this@toBuilder.attributes.toMutableMeta()
-}
-
 /**
  * Make a deep copy of this descriptor applying given transformation [block]
  */

dataforge-meta/src/commonMain/kotlin/space/kscience/dataforge/meta/descriptors/schemeDescriptor.kt

@@ -3,13 +3,15 @@ package space.kscience.dataforge.meta.descriptors
 import space.kscience.dataforge.meta.Scheme
 import space.kscience.dataforge.meta.SchemeSpec
 import space.kscience.dataforge.meta.ValueType
+import space.kscience.dataforge.misc.DFExperimental
 import kotlin.reflect.KProperty1
 import kotlin.reflect.typeOf
 
+@DFExperimental
 public inline fun <S : Scheme, reified T> MetaDescriptorBuilder.value(
     property: KProperty1<S, T>,
     noinline block: MetaDescriptorBuilder.() -> Unit = {},
-): MetaDescriptorBuilder = when (typeOf<T>()) {
+): Unit = when (typeOf<T>()) {
     typeOf<Number>(), typeOf<Int>(), typeOf<Double>(), typeOf<Short>(), typeOf<Long>(), typeOf<Float>() ->
         value(property.name, ValueType.NUMBER) {
             block()
@@ -34,9 +36,10 @@ public inline fun <S : Scheme, reified T> MetaDescriptorBuilder.value(
         multiple = true
         block()
     }
-    else -> item(property.name, block)
+    else -> node(property.name, block)
 }
 
+@DFExperimental
 public inline fun <S : Scheme, reified T : Scheme> MetaDescriptorBuilder.scheme(
     property: KProperty1<S, T>,
     spec: SchemeSpec<T>,

dataforge-meta/src/commonTest/kotlin/space/kscience/dataforge/meta/JsonMetaTest.kt

@@ -2,7 +2,7 @@ package space.kscience.dataforge.meta
 
 import kotlinx.serialization.json.*
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
-import space.kscience.dataforge.meta.descriptors.item
+import space.kscience.dataforge.meta.descriptors.node
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
@@ -32,7 +32,7 @@ class JsonMetaTest {
     }
 
     val descriptor = MetaDescriptor {
-        item("nodeArray") {
+        node("nodeArray") {
             indexKey = "index"
         }
     }

dataforge-meta/src/commonTest/kotlin/space/kscience/dataforge/meta/MetaDelegateTest.kt

@@ -20,7 +20,7 @@ class MetaDelegateTest {
         var myValue by string()
         var safeValue by double(2.2)
         var enumValue by enum(TestEnum.YES)
-        var inner by spec(InnerScheme)
+        var inner by scheme(InnerScheme)
 
         companion object : SchemeSpec<TestScheme>(::TestScheme)
     }

dataforge-workspace/src/commonMain/kotlin/space/kscience/dataforge/workspace/Task.kt

@@ -6,7 +6,7 @@ import space.kscience.dataforge.data.DataTree
 import space.kscience.dataforge.data.GoalExecutionRestriction
 import space.kscience.dataforge.meta.Meta
 import space.kscience.dataforge.meta.MetaRepr
-import space.kscience.dataforge.meta.Specification
+import space.kscience.dataforge.meta.MetaSpec
 import space.kscience.dataforge.meta.descriptors.Described
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
 import space.kscience.dataforge.misc.DfType
@@ -43,10 +43,10 @@ public interface Task<out T : Any> : Described {
 }
 
 /**
- * A [Task] with [Specification] for wrapping and unwrapping task configuration
+ * A [Task] with [MetaSpec] for wrapping and unwrapping task configuration
  */
 public interface TaskWithSpec<out T : Any, C : Any> : Task<T> {
-    public val spec: Specification<C>
+    public val spec: MetaSpec<C>
     override val descriptor: MetaDescriptor? get() = spec.descriptor
 
     public suspend fun execute(workspace: Workspace, taskName: Name, configuration: C): TaskResult<T>
@@ -55,11 +55,11 @@ public interface TaskWithSpec<out T : Any, C : Any> : Task<T> {
         execute(workspace, taskName, spec.read(taskMeta))
 }
 
-public suspend fun <T : Any, C : Any> TaskWithSpec<T, C>.execute(
-    workspace: Workspace,
-    taskName: Name,
-    block: C.() -> Unit = {},
-): TaskResult<T> = execute(workspace, taskName, spec(block))
+//public suspend fun <T : Any, C : Scheme> TaskWithSpec<T, C>.execute(
+//    workspace: Workspace,
+//    taskName: Name,
+//    block: C.() -> Unit = {},
+//): TaskResult<T> = execute(workspace, taskName, spec(block))
 
 public class TaskResultBuilder<in T : Any>(
     public val workspace: Workspace,
@@ -76,7 +76,6 @@ public class TaskResultBuilder<in T : Any>(
  * @param descriptor of meta accepted by this task
  * @param builder for resulting data set
  */
-@Suppress("FunctionName")
 public fun <T : Any> Task(
     resultType: KType,
     descriptor: MetaDescriptor? = null,
@@ -98,7 +97,6 @@ public fun <T : Any> Task(
     }
 }
 
-@Suppress("FunctionName")
 public inline fun <reified T : Any> Task(
     descriptor: MetaDescriptor? = null,
     noinline builder: suspend TaskResultBuilder<T>.() -> Unit,
@@ -116,10 +114,10 @@ public inline fun <reified T : Any> Task(
 @Suppress("FunctionName")
 public fun <T : Any, C : MetaRepr> Task(
     resultType: KType,
-    specification: Specification<C>,
+    specification: MetaSpec<C>,
     builder: suspend TaskResultBuilder<T>.(C) -> Unit,
 ): TaskWithSpec<T, C> = object : TaskWithSpec<T, C> {
-    override val spec: Specification<C> = specification
+    override val spec: MetaSpec<C> = specification
 
     override suspend fun execute(
         workspace: Workspace,
@@ -135,8 +133,7 @@ public fun <T : Any, C : MetaRepr> Task(
     }
 }
 
-@Suppress("FunctionName")
 public inline fun <reified T : Any, C : MetaRepr> Task(
-    specification: Specification<C>,
+    specification: MetaSpec<C>,
     noinline builder: suspend TaskResultBuilder<T>.(C) -> Unit,
 ): Task<T> = Task(typeOf<T>(), specification, builder)

dataforge-workspace/src/commonMain/kotlin/space/kscience/dataforge/workspace/WorkspaceBuilder.kt

@@ -7,8 +7,8 @@ import space.kscience.dataforge.context.Global
 import space.kscience.dataforge.data.*
 import space.kscience.dataforge.meta.Meta
 import space.kscience.dataforge.meta.MetaRepr
+import space.kscience.dataforge.meta.MetaSpec
 import space.kscience.dataforge.meta.MutableMeta
-import space.kscience.dataforge.meta.Specification
 import space.kscience.dataforge.meta.descriptors.MetaDescriptor
 import space.kscience.dataforge.meta.descriptors.MetaDescriptorBuilder
 import space.kscience.dataforge.misc.DFBuilder
@@ -68,7 +68,7 @@ public inline fun <reified T : Any> TaskContainer.task(
 }
 
 public inline fun <reified T : Any, C : MetaRepr> TaskContainer.task(
-    specification: Specification<C>,
+    specification: MetaSpec<C>,
     noinline builder: suspend TaskResultBuilder<T>.(C) -> Unit,
 ): PropertyDelegateProvider<Any?, ReadOnlyProperty<Any?, TaskReference<T>>> = PropertyDelegateProvider { _, property ->
     val taskName = Name.parse(property.name)