From: Robert Klemme <shortcutter@...>
Date: 2011-11-25T06:51:13+09:00
Subject: Re: How to Design Module Method?

On Thu, Nov 24, 2011 at 7:13 PM, Admin Tensor
<admin@tensor.heliohost.org> wrote:
> Hi,
>
> If I define a module method like this:
>
>  module MyMod
>    def MyMod.my_method
>    end
>  end
>
> then I can invoke it like this:
>
>  irb> MyMod.my_method
>  => nil
>
> but I cannot invoke my_method without the module name, even if I include
> the module:
>
>  irb> include MyMod
>  => Object
>  irb> my_method
>  NameError: undefined local variable or method `my_method' for
> main:Object
>
> Now, if I define the method like this:
>
>  module MyMod
>    def my_method
>    end
>  end
>
> then I cannot invoke my_method even with the module name:
>
>  irb> MyMod.my_method
>  NoMethodError: undefined method `my_method' for MyMod:Module
>
> but I can invoke it if I include the module:
>
>  irb> include MyMod
>  => Object
>  irb> my_method
>  => nil
>
> Therefore, my question is, is there any way so that both means of
> invoking work, i.e., for people who don't "include" the module they can
> type "MyMod.my_method", and for people who "include" the module they can
> simply type "my_method"?  (I am using Ruby 1.9.2.)

There are various methods, this is one of them:

irb(main):001:0> module Foo
irb(main):002:1> def bar;123;end
irb(main):003:1> extend self
irb(main):004:1> end
=> Foo
irb(main):005:0> Foo.bar
=> 123
irb(main):006:0> class X
irb(main):007:1> include Foo
irb(main):008:1> def test;bar;end
irb(main):009:1> end
=> nil
irb(main):010:0> X.new.test
=> 123

BUT: both uses are quite different.  When invoking on the module you
are basically using an algorithm which typically does not use context
(read: "state").  When invoking on the instance of a class which
includes the module then it can potentially use context (i.e. instance
state).  Both uses are quite different which is why I generally
suggest to not do this and keep aspects separate and not do this "dual
use".

Kind regards

robert



-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/