alias_methods.rb

class Object
  # This does not work on ruby 1.8.x because the methods are not returned
  # in the order they were defined. Also, under 1.8, the method names are
  # returned as strings, not symbols.

  # Identifies method aliases in the class and returns an array with
  # their symbols. This uses #methods, so it includes all methods
  # accessible in the object's ancestors.
  def alias_methods
    aliases = []
    ms = methods
    ms.each_with_index do |m, i|
      (i+1).upto(ms.length-1) do |t| 
        next if aliases.include? m
        aliases << ms[t] if method(m) == method(ms[t])
      end 
    end
    aliases
  end 

  # Returns an array of the aliases defined for the given method,
  # returns an empty array if no aliases are defined.
  def method_aliases(m)
    aliases = []
    alias_methods.each do |a| 
      aliases << a if method(m) == method(a)
    end 
    aliases
  end 

  # Returns the original method for the given alias, return nil if the
  # alias does not resolve to a method in the object.
  def resolve_alias(a)
    return unless is_alias?(a)
    methods.each {|m| return(m) if method(m) == method(a)}
  end 

  # Tests if the given method (symbol) is an alias to another
  # method in the object.
  def is_alias?(m)
    alias_methods.include? m
  end
end

test_aliases.rb

require "test/unit"
require File.expand_path '../alias_methods', __FILE__

class Foo
  def m_1; end
  def m_2; end
  def m_3; end

  alias :am_1 :m_1

  alias :am_2 :m_2
  alias :am_3 :m_2

  alias :am_4 :m_3
  alias :am_5 :m_3
  alias :am_6 :m_3
end

class TestMethodAliases < Test::Unit::TestCase
  def test_alias_methods
    o_aliases = Object.new.alias_methods
    f_aliases = Foo.new.alias_methods

    assert_equal( 6, (f_aliases - o_aliases).length )
    assert_equal( true, f_aliases.include?(:am_2) )
  end

  def test_method_aliases
    aliases = Foo.new.method_aliases(:m_3)
    assert_equal( 3, aliases.length )
    assert_equal( true, aliases.include?(:am_6) )
  end

  def test_resolve_alias
    assert_equal( :m_2, Foo.new.resolve_alias(:am_3) )
  end

  def test_resolve_alias_undefined
    assert_equal( nil, Foo.new.resolve_alias(:am_9) )
  end

  def test_is_alias
    assert_equal( true, Foo.new.is_alias?(:am_3) )
  end
end