Fix MutableMetaView.kt

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

@@ -2,14 +2,15 @@ package space.kscience.dataforge.meta
 
 import space.kscience.dataforge.names.Name
 import space.kscience.dataforge.names.NameToken
+import space.kscience.dataforge.names.parseAsName
 import space.kscience.dataforge.names.plus
 
 /**
- * A [Meta] child proxy that creates required nodes on write
+ * A [Meta] child proxy that creates required nodes on value write
  */
-public class MutableMetaView(
-    public val origin: MutableMeta,
-    public val path: Name
+private class MutableMetaView(
+    val origin: MutableMeta,
+    val path: Name
 ) : MutableMeta {
 
     override val items: Map<NameToken, MutableMeta>
@@ -23,18 +24,24 @@ public class MutableMetaView(
 
     override fun getOrCreate(name: Name): MutableMeta = MutableMetaView(origin, path + name)
 
-
     override fun set(name: Name, node: Meta?) {
-        set(path + name, node)
+        if (origin[path + name] == null && node?.isEmpty() == true) return
+        origin[path + name] = node
     }
 
-
     override fun equals(other: Any?): Boolean = Meta.equals(this, other as? Meta)
 
-
-    override fun hashCode(): Int  = Meta.hashCode(this)
+    override fun hashCode(): Int = Meta.hashCode(this)
 
     override fun toString(): String = Meta.toString(this)
 }
 
-public fun MutableMeta.view(name: Name): MutableMetaView = MutableMetaView(this, name)
+/**
+ * Create a view of this [MutableMeta] node that creates child items only when their values are written.
+ *
+ * The difference between this method and regular [getOrCreate] is that [getOrCreate] always creates and attaches node
+ * even if it is empty.
+ */
+public fun MutableMeta.view(name: Name): MutableMeta = MutableMetaView(this, name)
+
+public fun MutableMeta.view(name: String): MutableMeta = view(name.parseAsName())

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

@@ -59,7 +59,7 @@ private class ObservableMetaWrapper(
 
     fun removeNode(name: Name): Meta? {
         val oldMeta = get(name)
-        //don't forget to remove listener
+        //remember to remove listener
         oldMeta?.removeListener(this)
 
         return oldMeta

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

@@ -0,0 +1,25 @@
+package space.kscience.dataforge.meta
+
+import space.kscience.dataforge.names.asName
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class MutableMetaViewTest {
+    @Test
+    fun metaView() {
+        val meta = MutableMeta()
+        val view = meta.view("a".asName())
+
+        view["b"] = Meta.EMPTY
+
+        assertTrue { meta.items.isEmpty() }
+
+        view["c"] = Meta {
+            "d" put 22
+        }
+
+        assertEquals(22, meta["a.c.d"].int)
+    }
+
+}