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tree.rb
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tree.rb
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# A general-purpose library for implementing tree structures with arbitrary branching
# The arbitrary branching makes this something like the GoF "Composite Pattern"...
# To add application-specific functionality, subclass Tree::Node
# Written by Alex Dowad (alexinbeijing@gmail.com)
# The original version of this file lives on the Internet at https://github.com/alexdowad/showcase/blob/master/tree.rb
# Please copy, use, modify, and enjoy it freely, but keep this notice!
# If you modify, add "# Hacked by ..." below the above name(s)
# Our trees are immutable, BUT we provide mutable "views" of trees
# You can directly traverse the immutable trees downwards, or iterate over children of a node
# With a mutable view, you can also traverse upwards/right/left
# Get a mutable view of a tree with node.mutable
# After modifying, get back a new, immutable tree (rooted at the node which was used to create the mutable view) with view.immutable
# (Note: #immutable uses #dup to copy nodes as needed. So if you store application-specific data in
# nodes that needs to be copied, you must override #dup!)
# Mutable views proxy to the tree being viewed, so you can call other, application-specific node methods on them
# Immutable tree nodes define equality/hash code recursively based on their contents,
# but mutable views define equality/hash code by object identity (the default for Ruby)
# Nodes can either be "branch" or "leaf" nodes -- "branches" can have children, but "leaves" cannot
#################################
# Example usage:
# class MyLeaf < Tree::Node
# leaf_node
# end
# class MyBranch < Tree::Node
# end
# branch,leaf1,leaf2 = MyBranch.new,MyLeaf.new,MyLeaf.new
# view = branch.mutable
# view.add_child(leaf1)
# view.immutable
module Tree
class Node
def initialize(*children)
raise "#{self.class} can't have child nodes" if self.class.leaf?
@__children__ = children.freeze
end
def children
@__children__
end
def first_child
@__children__.first
end
def last_child
@__children__.last
end
def descendants(&block)
return enum_for(:descendants) if not block_given?
children do |node|
yield node
if node.respond_to? :descendants
node.descendants(&block)
end
end
end
def hash
@hash ||= @__children__.map(&:hash).hash ^ self.class.hash
end
def eql?(other)
return true if equal?(other)
return false if self.class != other.class
@__children__.eql?(other.children)
end
def ==(other)
return true if equal?(other)
return false if self.class != other.class
@__children__ == other.children
end
def self.inherited(cls)
cls.class_eval do
@__leaf__ = false
def self.leaf_node; @__leaf__ = true; end
def self.leaf?; @__leaf__; end
def self.branch?; !@__leaf__; end
end
end
end
class MutableNode
def initialize(path, node)
@path, @node, @prev, @next, @changed = path, node, nil, nil, false
end
def node
@node
end
def next
@next
end
def previous
@prev
end
alias :prev :previous
def parent
@path.last
end
def root
root = parent
root = root.parent while root.parent
root
end
def first_child
@first_child ||= begin
path_up = @path.dup << self
cs = @node.children.map { |n| MutableNode.new(path_up, n) }
cs.each_with_index { |c,i| c.instance_eval { @prev = cs[i-1]; @next = cs[i+1] }}
@last_child = cs.last
cs.first
end
end
def last_child
@last_child || (__first_child__; @last_child)
end
def children
return enum_for(:children) if not block_given?
current = first_child
(yield current; current = current.next) while current
end
def ancestors
return enum_for(:ancestors) if not block_given?
current = self.parent
(yield current; current = current.parent) while current
end
def siblings(&block)
return enum_for(:siblings) if not block_given?
preceding(&block)
following(&block)
end
def preceding
return enum_for(:preceding) if not block_given?
current = self.prev
(yield current; current = current.prev) while current
end
def following
return enum_for(:following) if not block_given?
current = self.next
(yield current; current = current.next) while current
end
def descendants(&block)
return enum_for(:descendants) if not block_given?
children do |node|
yield node
if node.respond_to? :descendants
node.descendants(&block)
end
end
end
def insert_next(node)
node = node.node if node.is_a?(MutableNode)
raise "Can't add #{node.class} after a node with no parent" if parent.nil?
new_node = MutableNode.new(@path, node)
this_node = self
new_node.instance_eval { @prev = this_node; @next = this_node.next }
@next.instance_eval { @prev = new_node } if @next
parent.instance_eval { @last_child = new_node } if parent.last_child.equal?(self)
@next = new_node
changed!
end
def insert_previous(node)
node = node.node if node.is_a?(MutableNode)
raise "Can't add #{node.class} after an node with no parent" if parent.nil?
new_node = MutableNode.new(@path, node)
this_node = self
new_node.instance_eval { @next = this_node; @prev = this_node.prev }
@prev.instance_eval { @next = new_node } if @prev
parent.instance_eval { @first_child = new_node } if parent.first_child.equal?(self)
@prev = new_node
changed!
end
def replace_with(node)
node = node.node if node.is_a?(MutableNode)
raise "#{node.class} can't replace an node with no parent" if parent.nil?
@node = node
@first_child = @last_child = nil
changed!
end
def remove
raise "Can't remove root node" if parent.nil?
this_node = self
next.instance_eval { @prev = this_node.prev }
prev.instance_eval { @next = this_node.next }
parent.instance_eval { @first_child = this_node.next } if parent.first_child.equal?(self)
parent.instance_eval { @last_child = this_node.prev } if parent.last_child.equal?(self)
changed!
end
def add_child(node)
node = node.node if node.is_a?(MutableNode)
if last_node
last_node.insert_next(node)
else
@first_child = @last_child = MutableNode.new(@path.dup << self, node)
changed!
end
end
def reject_children!
node = @first_child
while node
next_node = node.next
node.remove if yield node
node = next_node
end
end
def reject_descendants!(&block)
node = @first_child
while node
next_node = node.next
if yield node
node.remove
elsif node.respond_to? :reject_descendants!
node.reject_descendants!(&block)
end
node = next_node
end
end
def immutable
root.__tree__
end
protected
def __immutable__
if @changed
@node = @node.dup
@node.instance_eval { @__children__ = children.map(&:__tree__) }
@changed = false
end
@node
end
private
def changed!
@changed = false
parent.changed! if parent
end
end
end