Is it possible to identify aliased methods in Ruby?

Question

Often within the console, I'll interrogate an object

pp obj.methods.sort #or...
pp (obj.methods - Object.methods).sort

In Ruby it's pretty common for a developer to provide aliases for methods. I am wondering if there is a reflective way of identifying aliases so that I might be able to display aliased methods, something like...

array.aliased_methods #=> {:collect => :map, ...}

This would be helpful for being able to identify exactly how many things an object can do.

Answer 1

In Ruby 1.9, aliased instance methods will be eql?, so you can define:

class Module
  def aliased_methods
    instance_methods.group_by{|m| instance_method(m)}.
      map(&:last).keep_if{|symbols| symbols.length > 1}
  end
end

Now if you try it, you will get:

class Foo
  def bar; 42 end
  alias baz bar
  def hello; 42 end
end

Foo.aliased_methods # => [[:bar, :baz]]

Array.aliased_methods # => [[:inspect, :to_s], [:length, :size]]

Note that some pairs are missing, e.g. [:map, :collect]. This is due to a bug that is now fixed and will be in the next version (2.0.0) If it is important to you, you can roll your own group_by without using hashes or eql? and only using ==.