CODEWITHSUNDEEP
rubysingletonmetaprogramming
l__flex__l
l__flex__l

Reputation: 1438

Alias a method to a single object

I'm trying to define a singleton aliased method. As in:

name = 'Bob'
# I want something similar to this to work
name.define_singleton_method(:add_cuteness, :+)
name = name.add_cuteness 'by'

I'm sure I can pass a method object as a second parameter.

I wouldn't want to do it like this

name.define_singleton_method(:add_cuteness) { |val| self + val }

I want to alias the String#+ method not use it. Emphasis on alias, but sending the actual method object as a second parameter would be cool too.

Upvotes: 6

Views: 736

Answers (1)

ndnenkov
ndnenkov

Reputation: 36101

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

Upvotes: 6

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