How does the “#map(&proc)” idiom work when introspecting module classes?

Question

Presenting the Idiom

I found an interesting but unexplained alternative to an accepted answer. The code clearly works in the REPL. For example:

module          


        

Answer 1

Your sequence is equivalent to:

c_names = Foo.constants #=> ["Bar"]
cs = c_names.map { |c_name| Foo.__send__(:const_get, c_name) } #=> [Foo::Bar]
cs.select{ |c| Class === c } #=> [Foo::Bar]

You can consider Object#method as (roughly):

class Object
  def method(m)
    lambda{ |*args| self.__send__(m, *args) }
  end
end

grep is described here http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-grep

=== for Class (which is subclass of Module) is described here http://ruby-doc.org/core-1.9.3/Module.html#method-i-3D-3D-3D

UPDATE: And you need to grep because there can be other constants:

module Foo
  PI = 3.14
  ...
end

and you probably don't need them.