These class(es) ease the ability to implement a Composite pattern [GoF] and a supporting Visitor pattern [GoF]. Pattern::Composite extends Enumerable, allowing rich iteration across the children of the Composite. Composite patterns are useful anywhere there is a hierarchy or tree. Examples include organization structures, parse trees for expressions, and anytime a collection of a collection (of a collection, etc.) occurs.
require 'composite-ruby' class MyClass include Pattern::Composite ... end
Mixed-in methods include:
<<(child) - add a sub-component add(child) - alias for << each - iterating through children total(:accessor) - sum the values of the specified accessor of the leaves aggregate(:accessor) - return an array of all elements of the specified accessor of the leaves collecting(:accessor) - return a merged collection of all the collections from the leaves
In addition, recursive accessors can be created. For example for totaling the values in leaves:
class MyClass include Pattern::Composite recursive_total :var1, :var2, ... ... end
This creates recursive methods that return the total all the values of var1 in the leaves. See the RSpec test, spec/unbalanced_composite_spec.rb, for a comprehensive example of usage.
Support for Composite pattern, including generating methods for leaves for:
totals: recursive_total :var1, :var2, :method1, :method2 aggregating value answers: recursive_values :var3, :var4, :method3, :method4 collecting array answers: recursive_collecting :var5, :var6, :method5, :method6
No support of Visitor pattern (yet)
require 'composite-ruby' class MyClass include Pattern::Composite recursive_total :to_i, :to_f ... end x = MyClass.new 3, 4 x << 5 x.to_i # => 12
RSpec (if you want to run the tests)
sudo gem install composite-ruby
The path here was hardly direct. Key contributors to the journey were:
Erich Gamma and the rest of the Gang of Four [GoF] for Design Patterns
Eric Gold for beating me about the head with Smalltalk and patterns
Matz (Yukihiro Matsumoto) for inventing a cool language Ruby
Dave (Pragmatic) Thomas for talking about it
Obie Fernandez for bullying Ruby into ThoughtWorks
Roy Singham for listening to Obie
Neil Hutchinson (TrafficBroker) for creating an environment championing innovation
(The MIT License)
Copyright © 2009 Fred George
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