From: Robert Klemme <bob.news@...>
Date: 2003-12-09T17:22:02+09:00
Subject: Re: Adjusting the Scope of Blocks


"Gavin Sinclair" <gsinclair@soyabean.com.au> schrieb im Newsbeitrag
news:49755.203.185.214.34.1070949030.squirrel@webmail.imagineis.com...
> > Hi,
> >
> > Is there a way to give a block associated with a method call the same
> > scope  as if it were executing inside the method.
> >
> > ie.
> >
> > class Foo
> >    ACONST = 1
> >
> >    def input_flags
> >         @FLAG_SEL = INPUT
> >         yield
> >    end
> >
> >    def output_flags
> >         @FLAG_SEL = OUTPUT
> >         yield
> >    end
> >
> >    def set(flgs)
> >         set_flags(@FLAG_SEL, flgs)
> >    end
> > end
> >
> > f = Foo.new
> >
> > f.input_flags {
> >   set ACONST
> > }
> >
> > f.output_flags {
> >   set ACONST
> > }
>
>
> I've never done it myself, but you might try:

This works as expected.  Note however that with this approach method local
variables are not accessible.

>   class Foo
>     def input_flags(&block)
>       @FLAG_SEL = INPUT
>       instance_eval &block
>     end
>   end

You can of course yield all values that should be accessible for the
block.

Another approach is to use "eval" with a binding, although be warned that
this can have serious security implications:

def tester(code)
  foo="bar"
  b = binding
  eval( code, b )
end

tester "puts foo"
=> prints "bar"

But why don't you just make "input_flags" and "output_flags" accessors to
member variables?  Then you can do "foo.input_flags |= Foo::ACONST".

Or you define a special bit set type:

class Bitset
  attr_accessor :val
  def initialize(v=0); @val=0; end

  def set(x); @val|=x; end
  def toggle(x); @val^=x; end
  def reset(x); set(x); toggle(x); end
  def to_i; val; end
end

Kind regards

    robert