Modules as namespaces

ruby-talk
1

I'm trying to nest modules to create namespaces, but I'm not having
much luck. Let's say I have

module A
  module B
    def foo; @foo end
  end
end

class Foo
  include A
  def initialize; @foo = 'foo' end
  def bar; B::foo end
end

Calling Foo#bar raises "NoMethodError: undefined method `foo' for

Sam

···

A::B.Module". I would like to get "foo". What am I doing wrong?

2

Sam Stephenson wrote:

I'm trying to nest modules to create namespaces, but I'm not having
much luck. Let's say I have

You need to make foo a module method of B:

> module A
> module B
> def foo; @foo end

         def B::foo; @foo; end

> end
> end
>
> class Foo
> include A
> def initialize; @foo = 'foo' end
> def bar; B::foo end
> end

Calling Foo#bar raises "NoMethodError: undefined method `foo' for
A::B.Module". I would like to get "foo". What am I doing wrong?

Sam

The way you had it originally, you were defining an _instance_ method of B. If you had included B in some class, you could then call foo as an method of instances of that class.

3

[re-sending an answer that didn't seem to make it for some reason]

Hi --

I'm trying to nest modules to create namespaces, but I'm not having
much luck. Let's say I have

> module A
> module B
> def foo; @foo end
> end
> end
>
> class Foo
> include A
> def initialize; @foo = 'foo' end
> def bar; B::foo end
> end

Calling Foo#bar raises "NoMethodError: undefined method `foo' for
A::B.Module". I would like to get "foo". What am I doing wrong?

The notation B::foo mean's B's own foo method:

  module B
    def B.foo
      puts "hi"
    end
  end

  B::foo # hi

To get your Foo object to have the method B#foo in its path, you'd
have to include the module (A::B) in Foo, or extend your object with
it.

David

···

On Wed, 15 Sep 2004, Sam Stephenson wrote:

--
David A. Black
dblack@wobblini.net

4

Okay, I see. But now Foo#bar gives nil.

So mixing in a module doesn't mix-in other modules "inside it" in the same way?

Sam

···

On Wed, 15 Sep 2004 06:34:01 +0900, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:

You need to make foo a module method of B:
> module A
> module B
         def B::foo; @foo; end
> end
> end
The way you had it originally, you were defining an _instance_ method of
B. If you had included B in some class, you could then call foo as an
method of instances of that class.

5

Sam Stephenson wrote:

···

On Wed, 15 Sep 2004 06:34:01 +0900, Joel VanderWerf > <vjoel@path.berkeley.edu> wrote:

You need to make foo a module method of B:

module A
  module B

        def B::foo; @foo; end

  end
end

The way you had it originally, you were defining an _instance_ method of
B. If you had included B in some class, you could then call foo as an
method of instances of that class.

Okay, I see. But now Foo#bar gives nil.

So mixing in a module doesn't mix-in other modules "inside it" in the same way?

Nope. The namespace containment hierarchy is different from the inheritance hierarchy.

6

Got it. Thanks for the help!

Sam

···

On Wed, 15 Sep 2004 07:34:31 +0900, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:

Nope. The namespace containment hierarchy is different from the
inheritance hierarchy.