How to Identify Aliased Methods in Ruby

Is it possible to identify aliased methods in Ruby?

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 ==.

How to test method alias ruby

You can use Object#method.

Test.method(:b) == Test.method(:a)

Find which alias method is called in rails model

def net_stock_quantity(alias_used = :net_stock_quantity)
    method_called = caller[0]
    #some code
end

The method_called will contain the name of called alias.

Is there an elegant way to test if one instance method is an alias for another?

According to the documentation for Method,

Two method objects are equal if that
are bound to the same object and
contain the same body.

Calling Object#method and comparing the Method objects that it returns will verify that the methods are equivalent:

m.method(:bar) == m.method(:foo)

How can I obtain the aliases of of a method?

Not sure if iterating over all instance methods is considered "brute force", but this would work:

class Foo
  def bar
  end

  alias bar2 bar
  alias_method :bar3, :bar
end

Foo.instance_methods.select do |m|
  Foo.instance_method(m) == Foo.instance_method(:bar)
end
#=> [:bar, :bar2, :bar3]

Alias a method to a single object

Singleton methods are contained in that object's singleton class:

class Object
  def define_singleton_alias(new_name, old_name)
    singleton_class.class_eval do
      alias_method new_name, old_name
    end
  end
end

rob = 'Rob'
bob = 'Bob'
bob.define_singleton_alias :add_cuteness, :+

bob.add_cuteness 'by' # => "Bobby"
rob.add_cuteness 'by' # => NoMethodError

---

Object#define_singleton_method basically does something like this:

def define_singleton_method(name, &block)
  singleton_class.class_eval do
    define_method name, &block
  end
end

Assignment methods are not aliased properly

Setter methods need explicit receivers. Your code:

def attr= value ; a_attr= value ; end

is not calling the setter a_attr=; it is assigning a value to a local variable a_attr.

To do what you want, you need to do:

def attr= value; self.a_attr= value; end

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