From: Tom Sawyer <transami@...>
Date: 2002-07-22T19:35:39+09:00
Subject: Re: adding an argument to a proc

Kent,

yuk, that is nasty! neat hack though. i'll see if i can just make do
with having to have the argument - its only a minor inconvience.

have any ideas about my super in proc post? that one is kind of vital. i
don't know what i'll do if i can't figure that one out.

thanks!
~tom

On Mon, 2002-07-22 at 04:24, Kent Dahl wrote:
> Tom Sawyer wrote:
> > 
> > is there a way to add an argument to a proc after its creation?
> 
> Don't think so. Sounds like it would wreak a havoc of ambiguity on
> variable scope
>  
> > ex-
> > 
> > p = Proc.new { x + 5 }
> > px = Proc.new { |x| p.call(5) }
> > 
> > this won't work
> 
> You could perhaps be nasty and run eval on the binding of the block and
> setting the scope local variable explicitly, before calling the proc.
> 
> <CODE>
> x = nil # Has to exist in scope of block definition
> p1 = Proc.new { x + 5 }
> 
> # Define a wrapper Proc that sets the x to a number
> p2 = Proc.new {|y_uNiQuE_VarName| 
>   eval "old_x_uNiQuE_VarName = x", p1
>   eval "x=#{y_uNiQuE_VarName}", p1  # naive version
>   result = p1.call
>   eval "x=old_x_uNiQuE_VarName", p1
>   result
> }
> 
> # Less naive version that should work with any object
> p3 = Proc.new {|y_uNiQuE_VarName| 
>   eval "old_x_uNiQuE_VarName = x", p1
>   eval "x=ObjectSpace._id2ref(#{y_uNiQuE_VarName.id})", p1  # less naive
>   result = p1.call
>   eval "x=old_x_uNiQuE_VarName", p1
>   result
> }
> 
> puts p2.call(5)  #=> 10
> puts p3.call(15) #)=> 20
> 
> puts "Dang!" if x != nil
> </CODE>
> 
> -- 
> (\[ Kent Dahl ]/)_    _~_    __[ http://www.stud.ntnu.no/~kentda/ ]___/~
>  ))\_student_/((  \__d L b__/  NTNU - graduate engineering - 4. year  )
> ( \__\_�|�_/__/ ) _)Industrial economics and technological management(
>  \____/_�_\____/ (____engineering.discipline_=_Computer::Technology___)
> 
-- 
~transami

  _(")_  dobee dobee do...
   \v/  
   ^ ^