ImmutableList.Builder.subList should return a view of the builder.

Author: ilya-g

kotlinx-collections-immutable/src/main/kotlin/kotlinx/collections/immutable/ImmutableVectorList.kt

@@ -111,8 +111,8 @@ internal class ImmutableVectorList<out E> private constructor(private val impl:
 
         override fun set(index: Int, element: E): E = get(index).apply { mutate { it.with(index, element) } }
 
-        // TODO: make subList a view of this builder, rather than builder of the view
-        override fun subList(fromIndex: Int, toIndex: Int): Builder<E> = Builder(value, impl.subList(fromIndex, toIndex))
+        // to make subList a view of this builder, rather than builder of the view
+        //override fun subList(fromIndex: Int, toIndex: Int): Builder<E> = Builder(value, impl.subList(fromIndex, toIndex))
     }
 
 }

kotlinx-collections-immutable/tests/src/test/kotlin/kotlinx.collections.immutable/ImmutableListTest.kt

@@ -118,6 +118,16 @@ class ImmutableListTest {
         }
     }
 
+    @Test fun subListOfBuilder() {
+        val list = "abcxaxyz12".toImmutableList()
+        val builder = list.builder()
+        val subList = builder.subList(2, 5)
+        builder[4] = 'b'
+        assertEquals("cxb", subList.joinToString(""))
+        subList.replaceAll { it -> it + 1 }
+        assertEquals("abdycxyz12", builder.joinToString(""))
+    }
+
     fun <T> ImmutableList<T>.testMutation(operation: MutableList<T>.() -> Unit) {
         val mutable = this.toMutableList()
         val builder = this.builder()