From: Its Me <itsme213@...>
Date: 2004-04-08T06:04:18+09:00
Subject: Re: Idea: Simplified GTK


"Gregory Millam" <walker@lethalcode.net> wrote in message

> 2) So it doesn't require defining a new child of EzGtk Either done with a
class variable on class Object, as it is above, or use a global. But using
either isn't thread-safe, so Thread.current["storefunc"] would be thread
safe. - This is also, as the website 'Its me' pointed out, a dynamically
scoped variable.
>
>   So to accomplish (1), I'd just need to change my code to do this:
>
>   holdfunc = Thread.current["storefunc"]
>   Thread.current["storefunc"] = lambda { ... }
>   yield thewidget
>   Thread.current["storefunc"] = holdfunc

This would be another implementation basis for dynamically scoped vars. As
the pragprog site details, you would have to wrap some push/pop around a
stack of variable bindings, hold onto that stack in a Thread.current
variable, and then:

with_context (bindings) {...} # push onto dynamic bindings stack
find_in_context(var)        # lookup bindings stack from innermost to outer

One advantage this approach offers over Avi's callcc/catch/throw gem is that
you could, should such nastiness grab your fancy, even do the lookup in the
opposite direction. to make an outer binding can override an inner binding:

with_context(:var=>"outer") {
    with_context(:var=>"inner") {
        find_in_context(:var)    # ===> "outer"
    }
}

btw: I think some form of dynamic binding should be in the Ruby standard
libraries, just like resumable exceptions (whose implementation would
probably also use callcc/catch/throw).