newbie q on class Foo::Bar

[matt neuburg]

What's the point of a class-within-a-class? For example, I take it that
I can say:

class Foo
class Bar
def whatever
...

And then I can say

my_foo_bar = Foo::Bar.new

For example, isn't that what something like File::Stat is?

My question is, am I right about this, and if so, what's the point of
doing so? I take it that Bar is not magically related to Foo - it can't
see Foo's methods or anything like that, can it? So is this merely a way
of using a class (Foo) as a namespace so that related classes (like Bar)
are all in one place? Thx - m.

 

[dblack]

Hi --

One reason is to create a class that is private. You may be aware that one
wants to separate results from implementation (separate the result from the
method used to produce the result), this can extend to classes that need to
exist, but don't need to be made available as part of the interface. That
way, the programmer can change the class without having to ask what
external effects this might have.

The nesting won't give you privacy, though; the class can still be
accessed from outside. You could of course not document it, but
that's no more true of a nested class than a non-nested one.


David

--
David A. Black | (e-mail address removed)
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

 

[matt neuburg]

Hi --



The nesting won't give you privacy, though; the class can still be
accessed from outside. You could of course not document it, but
that's no more true of a nested class than a non-nested one.

I'm glad you're weighing in here, since, though this is a common enough
Ruby idiom, Rails is the case in point that got me thinking about this.
So, for example, have ActionController::Base and
ActionController::AbstractRequest something in common (other than being
packaged in the same namespace)? Thx - m.