Metaclass/Singleton class question.

rubyonrails-talk
1

I understand that (class << self; self; end) returns the singelton class of object that is calling it but why would use that instead of self << MyClass ...?

For example, arent these all equivalent?

class << String   def foo     puts "foo"   end end

class String   class << self     def foo       puts "foo"     end   end end

class String   (class << self; self; end).module_eval do      def foo        puts "foo"      end   end end

So why would you use the more obscure (class << self; self; end) technique? Can someone please explain.

2

I understand that (class << self; self; end) returns the singelton
class of object that is calling it but why would use that instead of self << MyClass ...?

For example, arent these all equivalent?

class << String def foo    puts "foo" end end

class String class << self    def foo      puts "foo"    end end end

class String (class << self; self; end).module_eval do     def foo       puts "foo"     end end end

So why would you use the more obscure (class << self; self; end) technique? Can someone please explain.

if self isn't a class for example

class Object    def meta      (class << self; self; end)    end end

x = "123" x.meta.module_eval do    def foo      puts "foo"    end end

x.foo

you could of course have just done

def x.foo    puts "foo" end

but sometimes you want to more than just add a method.

Fred