Help with object scope

ruby-talk
1

module M
  class C
   def self.blah
   end
  end
end

module M2
  include M
  class TestM
    def setup; C.blah; end
  end
end

Won't work because the C tries to refer to TestM::C, which doesn't
exist.

Previously, when you did an "include M" you included the module into
Kernel.

Since:
  TestM is an instance of Class
  Class is an instance of Object
  You've included M in Object, causing Object::C to be created

So, in that case TestM::C exists.

···

-----Original Message-----
From: list-bounce@example.com
[mailto:list-bounce@example.com] On Behalf Of List Recv
Sent: Wednesday, 21 December 2005 4:14 PM
To: ruby-talk ML
Subject: Help with object scope

I'm having a really tough time with Ruby's scope (modules, include,
etc.).

I had a file, in short:

module M
  class C
  end
end

# Unit Tests
include M
class TestM
def setup; C.blah; end
end

Works great.

*However*, if I wrap the unit tests in their own module, then
ruby can
no longer find class C. Why? Didn't I include module M? I'm really
confused here.

If you want the full source, I can post it.

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2

I see.

So,
1) How do I call C from class TestM without explicitly using its
namespace (M:C)? Is there no way? I don't want to modify Kernel or
anything, just have class C available.

2) Could you explain exactly what a Module is? A namespace? A set of
methods without a home? I'm really confused... (I know that
module_define and class_define are synonomous, which is even more
confusing...)

Daniel Sheppard wrote:

···

module M
  class C
   def self.blah
   end
  end
end

module M2
  include M
  class TestM
    def setup; C.blah; end
  end
end

Won't work because the C tries to refer to TestM::C, which doesn't
exist.

Previously, when you did an "include M" you included the module into
Kernel.

Since:
  TestM is an instance of Class
  Class is an instance of Object
  You've included M in Object, causing Object::C to be created

So, in that case TestM::C exists.

I had a file, in short:
end

Works great.

*However*, if I wrap the unit tests in their own module, then
ruby can
no longer find class C. Why? Didn't I include module M? I'm really
confused here.

If you want the full source, I can post it.

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3

List Recv wrote:

2) Could you explain exactly what a Module is? A namespace? A set of methods without a home? I'm really confused... (I know that module_define and class_define are synonomous, which is even more confusing...)

A little bit of both, actually. Here's a good description of what a Module is: http://www.rubycentral.com/book/tut_modules.html

4

List Recv wrote:

So,
1) How do I call C from class TestM without explicitly using its namespace (M:C)? Is there no way? I don't want to modify Kernel or anything, just have class C available.

Try this instead:

class TestM
  include M
  def setup; C.blah; end
end

A module is a set of instance methods and constants. It can either be used as a namespace or mix-in functionality. (For the latter you are collecting similar methods / constants together in one Module so you can add them to your own classes or objects easily.)

mod_or_cls.include(mod) will add all constants and instance methods of mod to mod_or_cls.

obj.extend(mod) will add all constants and instance methods of mod to an object itself.

Here's a sample:

module HalfString
   def half()
     self[0, length / 2]
   end
end

str = "foobar"
str.half() # raises NoMethodError
str.extend(HalfString)
str.half() # => "foo"

"hello".half() # raises NoMethodError

You can't ever include classes. You can only inherit from them.

···

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5

Try this instead:

class TestM
  include M
  def setup; C.blah; end
end

I see.

So, that's the equivalent of:

class TestM
  class C; ... ; end
  def setup; C.blah ; end
end

What exactly does it mean to nest a class?
I know that you cannot define a class within a method (not sure why)?

Also, is require the same thing as "copy and paste dynamically", or does
it drop down to the global namespace, or do something else?

···

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