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117 lines
4.0 KiB
Dart
117 lines
4.0 KiB
Dart
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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/// An abstract node in a tree
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///
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/// AbstractNode has as notion of depth, attachment, and parent, but does not
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/// have a model for children.
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///
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/// * When a subclass is changing the parent of a child, it should
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/// call either parent.adoptChild(child) or parent.dropChild(child)
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/// as appropriate. Subclasses should expose an API for
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/// manipulating the tree if you want to (e.g. a setter for a
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/// 'child' property, or an 'add()' method to manipulate a list).
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///
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/// * You can see the current parent by querying 'parent'.
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///
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/// * You can see the current attachment state by querying
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/// 'attached'. The root of any tree that is to be considered
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/// attached should be manually attached by calling 'attach()'.
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/// Other than that, don't call 'attach()' or 'detach()'. This is
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/// all managed automatically assuming you call the 'adoptChild()'
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/// and 'dropChild()' methods appropriately.
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///
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/// * Subclasses that have children must override 'attach()' and
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/// 'detach()' as described below.
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///
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/// * Nodes always have a 'depth' greater than their ancestors'.
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/// There's no guarantee regarding depth between siblings. The
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/// depth of a node is used to ensure that nodes are processed in
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/// depth order. The 'depth' of a child can be more than one
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/// greater than the 'depth' of the parent, because the 'depth'
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/// values are never decreased: all that matters is that it's
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/// greater than the parent. Consider a tree with a root node A, a
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/// child B, and a grandchild C. Initially, A will have 'depth' 0,
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/// B 'depth' 1, and C 'depth' 2. If C is moved to be a child of A,
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/// sibling of B, then the numbers won't change. C's 'depth' will
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/// still be 2. This is all managed automatically assuming you call
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/// 'adoptChild()' and 'dropChild()' appropriately.
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class AbstractNode {
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// AbstractNode represents a node in a tree.
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// The AbstractNode protocol is described in README.md.
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int _depth = 0;
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/// The depth of this node in the tree.
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///
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/// The depth of nodes in a tree monotonically increases as you traverse down
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/// the trees.
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int get depth => _depth;
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/// Call only from overrides of [redepthChildren]
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void redepthChild(AbstractNode child) {
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assert(child._attached == _attached);
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if (child._depth <= _depth) {
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child._depth = _depth + 1;
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child.redepthChildren();
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}
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}
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/// Override this function in subclasses with child nodes to call
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/// redepthChild(child) for each child. Do not call directly.
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void redepthChildren() { }
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bool _attached = false;
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/// Whether this node is in a tree whose root is attached to something.
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bool get attached => _attached;
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/// Mark this node as attached.
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///
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/// Typically called only from the parent's attach(), and to mark the root of
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/// a tree attached.
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void attach() {
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_attached = true;
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}
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/// Mark this node as detached.
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///
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/// Typically called only from the parent's detach(), and to mark the root of
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/// a tree detached.
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void detach() {
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_attached = false;
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}
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AbstractNode _parent;
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/// The parent of this node in the tree.
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AbstractNode get parent => _parent;
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/// Subclasses should call this function when they acquire a new child.
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void adoptChild(AbstractNode child) {
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assert(child != null);
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assert(child._parent == null);
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assert(() {
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AbstractNode node = this;
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while (node.parent != null)
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node = node.parent;
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assert(node != child); // indicates we are about to create a cycle
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return true;
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});
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child._parent = this;
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if (attached)
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child.attach();
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redepthChild(child);
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}
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/// Subclasses should call this function when they lose a child.
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void dropChild(AbstractNode child) {
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assert(child != null);
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assert(child._parent == this);
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assert(child.attached == attached);
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child._parent = null;
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if (attached)
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child.detach();
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}
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}
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