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This post originated from an RSS feed registered with Ruby Buzz
by Matt Williams.
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Original Post: Watching changes
Feed Title: Ruby Blender
Feed URL: http://feeds2.feedburner.com/RubyBlender
Feed Description: This blog contains short-ish ruby tips, hints, and techniques.
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The ruby2ruby gem allows you to peer into a class's methods and watch changes due to metaprogramming.
ruby2ruby is a gem created by the Seattle Ruby Brigade. You can install it, like any other gem, with gem install ruby2ruby. Once installed, it lets you peer inside a Class' methods.
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$ irb
irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'ruby2ruby'
=> true
irb(main):003:0> class Foo
irb(main):004:1> attr_accessor :fud
irb(main):005:1> def initialize(fud)
irb(main):006:2> @fud = fud
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):009:0> Ruby2Ruby.translate Foo
=> "class Foo < Object\n attr_reader :fud\n \n attr_writer :fud\n \n def initialize(fud)\n @fud = fud\n end\nend"
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Here I've created a simple class. One thing that is interesting, the interpreter expands attr_accessor into both attr_reader and attr_writer for me automatically. One of the requirements of Ruby2Ruby is that it works on Classes, not on instances:
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irb(main):010:0> f=Foo.new(5)
=> #<Foo:0x2b82e560d608 @fud=5>
irb(main):011:0> Ruby2Ruby.translate f
NoMethodError: undefined method `instance_methods' for #<Foo:0x2b82e560d608 @fud=5>
from /usr/lib/ruby/gems/1.8/gems/ParseTree-2.1.1/lib/parse_tree.rb:115:in `parse_tree'
from /usr/lib/ruby/gems/1.8/gems/ParseTree-2.1.1/lib/parse_tree.rb:99:in `parse_tree'
from /usr/lib/ruby/gems/1.8/gems/ParseTree-2.1.1/lib/parse_tree.rb:71:in `translate'
from /usr/lib/ruby/gems/1.8/gems/ruby2ruby-1.1.8/lib/ruby2ruby.rb:31:in `translate'
from (irb):11
irb(main):012:0> Ruby2Ruby.translate f.class
=> "class Foo < Object\n attr_reader :fud\n \n attr_writer :fud\n \n def initialize(fud)\n @fud = fud\n end\nend"
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We can compare the code as it changes, too:
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irb(main):013:0> class Foo
irb(main):014:1> def something(bar)
irb(main):015:2> puts bar
irb(main):016:2> end
irb(main):017:1> end
=> nil
irb(main):018:0> Ruby2Ruby.translate Foo
=> "class Foo < Object\n attr_reader :fud\n \n attr_writer :fud\n \n def initialize(fud)\n @fud = fud\n end\n \n def something(bar)\n puts(bar)\n end\nend"
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There's a lot more which can be done here, and it will be the subject of a further entry.
Read: Watching changes
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