From: Matthew Kerwin <matthew@...>
Date: 2012-04-21T12:15:50+09:00
Subject: Re: Why must I know whether I extend a class or a module?

On 21/04/2012, Intransition <transfire@gmail.com> wrote:
>
>
> On Friday, April 20, 2012 8:12:37 PM UTC-4, Matthew Kerwin wrote:
>>
>> On 20 April 2012 13:53, Intransition <transfire@gmail.com> wrote:
>> > The forced distinction only serves to take that flexibility away from
>> > the
>> > programmer.
>>
>> Is there not overhead associated with that distinction? I haven't
>> actually looked into it, but I'd assume that Modules are a lot more
>> light-weight than Classes, because of the things that can't be done
>> with them.
>>
> The Class class is subclass of Module and is almost devoid of it's own
> methods.

Fair enough. Must be a pragmatism issue then. Unless the cost of
discovering and defining constructors and initializers is somehow more
than we'd expect.

What about multiple inheritance? Is/should it be valid to mix in a
class instead of a module?  Actually, what happens right now if you
define a class with no initializer, and mix in a module that defines
__initialize ?

>> > There are other benefits too in that removing the distinction would
>> > allow
>> > auto instantiation, e.g.
>> >
>> >     class Foo::Bar
>> >     end
>> >
>> > Would work just fine, even though no `Foo` has been defined separately.
>> This
>> > can be especially nice when requiring sub-files.
>>
>> I can see that this would be convenient, but it also makes me cringe.
>> You're defining a namespace Foo without ever explicitly defining it.
>> Why? What's its purpose?  How and where is it documented?  I can't
>> make my gut instinct accept this as anything but a bad idea.
>
> Typically that would be the case -- the encasing module/class would be
> defined *ultimately*. This way it just doesn't have to be done prior to
> classes/module internal to it.
>
> For example in project I often need adapters.
>
>   class MyApp::Adapters::Foo
>   class MyApp::Adapters::Bar
>   ...
>
> In the myapp/adapters.rb I've would like to write:
>
>   require 'myapp/adapters/foo'
>   require 'myapp/adapters/bar'
>
>   module MyApp::Adapters
>     ...
>   end
>
> But instead I have to do:
>
>   module MyApp::Adapters
>     ...
>   end
>
>   require 'myapp/adapters/foo'
>   require 'myapp/adapters/bar'
>
> I don't like requires at the bottom.

Or the alternative:

require 'myapp/adapters/core'
require 'myapp/adapters/foo'
require 'myapp/adapters/bar'
module MyApp::Adapters
  # stuff that uses foo and bar
end

> Even so, there are times when it doesn't really matter. If for instance my
> MyApp::Adapters module had no contents other then the adapter classes, then
> it really makes no difference.

I guess I have a hole in my instinctive response for the right
approach to 'modules as a namespace', since I usually use them as
interfaces/multiple-inheritance/mixins.

-- 
  Matthew Kerwin, B.Sc (CompSci) (Hons)
  http://matthew.kerwin.net.au/

  "You'll never find a programming language that frees
  you from the burden of clarifying your ideas." - xkcd