From: Yuh-Ruey Chen <maian330@...>
Date: 2008-11-01T04:34:00+09:00
Subject: Re: How to access to local variables in enclosing scopes?

On Oct 31, 2:18 pm, Stefan Lang <perfectly.normal.hac...@gmail.com>
wrote:
> 2008/10/31 Yuh-Ruey Chen <maian...@gmail.com>:
>
>
>
> > The difference that the local variable doesn't have to be defined in
> > global scope. Only child scopes should have access to that local
> > variable.
>
> > def foo
> >        a = 10
> >        def bar
> >                # should somehow be able to access a
> >        end
> >        bar
> > end
> > foo
> > # here, we should not be able to access foo's a, but if there is
> > another a in scope, we can access that
>
> > Or to put it in Python:
>
> > a = 20
> > def foo():
> >        a = 10
> >        def bar():
> >                print a # prints 10
> >        bar()
> > foo()
> > print a # prints 20
>
> The first assignment to a creates a _module_ scoped variable in Python.
> It is _not_ local, it can very well be accessed from anywhere via
>
>     import some_module
>     some_module.a

Well then just wrap that example in another function:

def scope()
	a = 20
	def foo():
		a = 10
		def bar():
			print a # prints 10
		bar()
	foo()
	print a # prints 20
scope()

My point was that scopes nest as expected.

> Since it's a bad idea anyway to reassign such variables
> (metaprogramming might be an exception), you can use
> Ruby's constants for this purpose:
>
>     module MyModule
>
>         A = 20
>
>         # can access A from anywhere within MyModule,
>         # including method definitions, nested classes, etc.
>
>     end
>
>     puts MyModule::A  # access from outside of MyModule
>
> At least anything that looks like local variable assignment
> in Ruby is actually local variable assignment. The thing to
> learn is that "module", "class" and "def" create new, empty
> local scopes, they have no enclosing scope with regards to
> local variables.
>
> It is generally a better idea to genuinely try to understand
> a new language and its idioms instead of bending it to ones
> expectations from the beginning.
>
> Stefan

I am trying to understand Ruby with some metaprogramming practice. But
I still feel that this is a really backwards step in language design.

It's like telling me I should use GOTO in original BASIC instead of
trying to bend the language to simulate while loops. Would any sane
modern programmer do that?