Composition

CustomTreeComposition

@Suppress("unused")
@Sampled
fun CustomTreeComposition() {
    // Provided we have a tree with a node base type like the following
    abstract class Node {
        val children = mutableListOf<Node>()
    }

    // We would implement an Applier class like the following, which would teach compose how to
    // manage a tree of Nodes.
    class NodeApplier(root: Node) : AbstractApplier<Node>(root) {
        override fun insertTopDown(index: Int, instance: Node) {
            current.children.add(index, instance)
        }

        override fun insertBottomUp(index: Int, instance: Node) {
            // Ignored as the tree is built top-down.
        }

        override fun remove(index: Int, count: Int) {
            current.children.remove(index, count)
        }

        override fun move(from: Int, to: Int, count: Int) {
            current.children.move(from, to, count)
        }

        override fun onClear() {
            root.children.clear()
        }
    }

    // A function like the following could be created to create a composition provided a root Node.