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comp.lang.ruby

code organization

Li Chen

6/6/2009 4:07:00 PM

Hi all,

What are the differences bewteen the following code organization?
What situations are preferred by each one?

Thanks,

Li

#######code 1#############
module A
class B end
class C end
end



#######code 2#############
class B
include module A
end

class C
include module A
end
--
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4 Answers

Brian Candler

6/6/2009 4:54:00 PM

0

Li Chen wrote:
> What are the differences bewteen the following code organization?
> What situations are preferred by each one?

In code 1, module A is just acting as a namespace, so that you have two
classes, A::B and A::C. This is useful to ensure that your class names
don't stomp on anyone else's use of the same names. All you have to do
is ensure name A is unique.

Code 2 doesn't run as it stands, so you need to rewrite as:

module A; end

class B
include module A
end

class C
include module A
end

In this case, instance methods defined in module A are available in both
class B and class C. This is almost the same as subclassing B and C from
class A. B and C also get access to any constants defined in the A
namespace, without needing the A:: prefix.

So in summary: they achieve two completely different ends (namespace
separation, and method sharing, respectively)
--
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Li Chen

6/6/2009 6:00:00 PM

0

Brian Candler wrote:
> So in summary: they achieve two completely different ends (namespace
> separation, and method sharing, respectively)

Hi Brian,

Thank you so much.

As I recall correctly module has two major funtions/purposes:
1) namespace separation 2) mixin. So you mean in the second code it
works as a mixin or method sharing?


Li

--
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matt

6/6/2009 7:29:00 PM

0

Li Chen <chen_li3@yahoo.com> wrote:

> Hi all,
>
> What are the differences bewteen the following code organization?
> What situations are preferred by each one?
>
> Thanks,
>
> Li
>
> #######code 1#############
> module A
> class B end
> class C end
> end
>
>
>
> #######code 2#############
> class B
> include module A
> end
>
> class C
> include module A
> end

They are totally different, and they illustrate the two main purposes of
a module. Neither is legal as you have it so I will change the code to
make it legal.

##### 1 ######

module A
class B
end
end
A::B.new

A is a namespace, so you must say A::B from outside module A to refer to
B.

##### 2 #####

module A
def hello
p "howdy"
end
end
class B
include A
end
B.new.hello

Module A's instance methods are copied into class B as instance methods
("mixin").

m.

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Brian Candler

6/7/2009 5:37:00 PM

0

Li Chen wrote:
> As I recall correctly module has two major funtions/purposes:
> 1) namespace separation 2) mixin. So you mean in the second code it
> works as a mixin or method sharing?

Yes, mixin or method sharing (two terms to describe the same thing)

Re-reading, there's another error I didn't fix in that example: it
should say "include A" not "include module A"
--
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