Meta converters return non-nullables

CHANGELOG.md

@@ -6,6 +6,7 @@
 - Added separate `Meta`, `SealedMeta` and `ObservableMutableMeta` builders.
 
 ### Changed
+- Meta converter `metaToObject` returns a non-nullable type. Additional method `metaToObjectOrNull` for nullable return.
 - Kotlin 1.9.20.
 - Migrated from ktor-io to kotlinx-io.
 - `MutableMeta` builder now returns a simplified version of meta that does not hold listeners. 

build.gradle.kts

@@ -8,7 +8,7 @@ plugins {
 
 allprojects {
     group = "space.kscience"
-    version = "0.6.3-dev-1"
+    version = "0.7.0-dev-1"
 }
 
 subprojects {

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

@@ -6,74 +6,77 @@ import space.kscience.dataforge.meta.*
  * A converter of generic object to and from [Meta]
  */
 public interface MetaConverter<T> {
-    public fun metaToObject(meta: Meta): T?
+
+    /**
+     * Attempt conversion of [meta] to an object or return null if conversion failed
+     */
+    public fun metaToObjectOrNull(meta: Meta): T?
+
+    public fun metaToObject(meta: Meta): T =
+        metaToObjectOrNull(meta) ?: error("Meta $meta could not be interpreted by $this")
+
     public fun objectToMeta(obj: T): Meta
 
     public companion object {
 
         public val meta: MetaConverter<Meta> = object : MetaConverter<Meta> {
-            override fun metaToObject(meta: Meta): Meta = meta
+            override fun metaToObjectOrNull(meta: Meta): Meta = meta
             override fun objectToMeta(obj: Meta): Meta = obj
         }
 
         public val value: MetaConverter<Value> = object : MetaConverter<Value> {
-            override fun metaToObject(meta: Meta): Value? = meta.value
+            override fun metaToObjectOrNull(meta: Meta): Value? = meta.value
             override fun objectToMeta(obj: Value): Meta = Meta(obj)
         }
 
         public val string: MetaConverter<String> = object : MetaConverter<String> {
-            override fun metaToObject(meta: Meta): String? = meta.string
+            override fun metaToObjectOrNull(meta: Meta): String? = meta.string
             override fun objectToMeta(obj: String): Meta = Meta(obj.asValue())
         }
 
         public val boolean: MetaConverter<Boolean> = object : MetaConverter<Boolean> {
-            override fun metaToObject(meta: Meta): Boolean? = meta.boolean
+            override fun metaToObjectOrNull(meta: Meta): Boolean? = meta.boolean
             override fun objectToMeta(obj: Boolean): Meta = Meta(obj.asValue())
         }
 
         public val number: MetaConverter<Number> = object : MetaConverter<Number> {
-            override fun metaToObject(meta: Meta): Number? = meta.number
+            override fun metaToObjectOrNull(meta: Meta): Number? = meta.number
             override fun objectToMeta(obj: Number): Meta = Meta(obj.asValue())
         }
 
         public val double: MetaConverter<Double> = object : MetaConverter<Double> {
-            override fun metaToObject(meta: Meta): Double? = meta.double
+            override fun metaToObjectOrNull(meta: Meta): Double? = meta.double
-
             override fun objectToMeta(obj: Double): Meta = Meta(obj.asValue())
         }
 
         public val float: MetaConverter<Float> = object : MetaConverter<Float> {
-            override fun metaToObject(meta: Meta): Float? = meta.float
+            override fun metaToObjectOrNull(meta: Meta): Float? = meta.float
-
             override fun objectToMeta(obj: Float): Meta = Meta(obj.asValue())
         }
 
         public val int: MetaConverter<Int> = object : MetaConverter<Int> {
-            override fun metaToObject(meta: Meta): Int? = meta.int
+            override fun metaToObjectOrNull(meta: Meta): Int? = meta.int
-
             override fun objectToMeta(obj: Int): Meta = Meta(obj.asValue())
         }
 
         public val long: MetaConverter<Long> = object : MetaConverter<Long> {
-            override fun metaToObject(meta: Meta): Long? = meta.long
+            override fun metaToObjectOrNull(meta: Meta): Long? = meta.long
-
             override fun objectToMeta(obj: Long): Meta = Meta(obj.asValue())
         }
 
         public inline fun <reified E : Enum<E>> enum(): MetaConverter<E> = object : MetaConverter<E> {
             @Suppress("USELESS_CAST")
-            override fun metaToObject(meta: Meta): E = meta.enum<E>() as? E ?: error("The Item is not a Enum")
+            override fun metaToObjectOrNull(meta: Meta): E = meta.enum<E>() as? E ?: error("The Item is not a Enum")
 
             override fun objectToMeta(obj: E): Meta = Meta(obj.asValue())
         }
 
         public fun <T> valueList(
             writer: (T) -> Value = { Value.of(it) },
-            reader: (Value) -> T
+            reader: (Value) -> T,
         ): MetaConverter<List<T>> =
             object : MetaConverter<List<T>> {
-                override fun metaToObject(meta: Meta): List<T> =
+                override fun metaToObjectOrNull(meta: Meta): List<T>? = meta.value?.list?.map(reader)
-                    meta.value?.list?.map(reader) ?: error("The item is not a value list")
 
                 override fun objectToMeta(obj: List<T>): Meta = Meta(obj.map(writer).asValue())
             }

gradle.properties

@@ -6,5 +6,5 @@ kotlin.mpp.stability.nowarn=true
 kotlin.incremental.js.ir=true
 kotlin.native.ignoreDisabledTargets=true
 
-toolsVersion=0.15.0-kotlin-1.9.20-RC
+toolsVersion=0.15.0-kotlin-1.9.20-RC2
 #kotlin.experimental.tryK2=true