add copy method to descriptors

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Yaml meta format based on yaml.kt
 - `Path` builders
 - Special ValueType for lists
+- `copy` method to descriptors
 
 ### Changed
 - `ListValue` and `DoubleArrayValue` implement `Iterable`.

dataforge-meta/src/commonMain/kotlin/hep/dataforge/meta/Config.kt

@@ -94,7 +94,11 @@ public class Config() : AbstractMutableMeta<Config>(), ObservableItemProvider {
 
 public operator fun Config.get(token: NameToken): MetaItem<Config>? = items[token]
 
-public fun Meta.asConfig(): Config = this as? Config ?: Config().also { builder ->
+/**
+ * Create a mutable copy of this [Meta]. The copy is created event if initial [Meta] is a [Config].
+ * Listeners are not preserved
+ */
+public fun Meta.toConfig(): Config = Config().also { builder ->
     this.items.mapValues { entry ->
         val item = entry.value
         builder[entry.key.asName()] = when (item) {
@@ -103,3 +107,8 @@ public fun Meta.asConfig(): Config = this as? Config ?: Config().also { builder
         }
     }
 }
+
+/**
+ * Return this [Meta] as [Config] if it is [Config] and create a new copy otherwise
+ */
+public fun Meta.asConfig(): Config = this as? Config ?: toConfig()

dataforge-meta/src/commonMain/kotlin/hep/dataforge/meta/descriptors/ItemDescriptor.kt

@@ -38,6 +38,8 @@ public sealed class ItemDescriptor(public val config: Config) {
      */
     public var indexKey: String by config.string(DEFAULT_INDEX_KEY)
 
+    public abstract fun copy(): ItemDescriptor
+
     public companion object{
         public const val DEFAULT_INDEX_KEY: String = "@index"
     }
@@ -180,6 +182,8 @@ public class NodeDescriptor(config: Config = Config()) : ItemDescriptor(config)
         value(name.toName(), block)
     }
 
+    override fun copy(): NodeDescriptor = NodeDescriptor(config.toConfig())
+
     public companion object {
 
         internal val ITEM_KEY: Name = "item".asName()
@@ -281,6 +285,8 @@ public class ValueDescriptor(config: Config = Config()) : ItemDescriptor(config)
     public fun allow(vararg v: Any) {
         this.allowedValues = v.map { Value.of(it) }
     }
+
+    override fun copy(): ValueDescriptor = ValueDescriptor(config.toConfig())
 }
 
 /**