From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-10-04T16:59:40+09:00
Subject: Re: Specifying local and external block parameters (that old chestnut)

On Fri, Oct 04, 2002 at 11:38:46AM +0900, Hal E. Fulton wrote:
> ----- Original Message -----
> From: "Gavin Sinclair" <gsinclair@soyabean.com.au>
> > Thus, if 'a' and 'c' are regular parameters and 'b' is an external variable,
> > then one could write
> >
> >   collection.each do |a,:b,c|
> >     ...
> >   end

See my note on this syntax in my original reply to Gavin :-)

> 
> One problem is that it's not just a simple variable. It
> can be anything that responds to assignment. For example,
> an accessor:
> 
>   0.upto(99) {|frame.scroll| sleep 0.1}

This works unchanged if you accept ':' as a local scope indicator, only
to be used on variables (not on accesor methods, as it'd be
meaningless), so Ruby would choke on 

  0.upto(99) {|:frame.scroll| sleep 0.1}

as anyway what you really want is 

  0.upto(99) {|frame.scroll| sleep 0.1}


> > I'd like to put a question to the audience :)  Does anyone actually have a
> need
> > to use non-local block parameters?  Ever?
> 
> The above is an example.
> 
> Also what if I want the last value(s) of a loop?
> 
>   x,i = nil
>   myobj.each_with_index do |x,i|
>     # process...
>     break if some_condition
>     # more processing...
>   end
> 
>   last_obj = x
>   last_index = i
> 
> Yes, I *could* save them off in different variables
> right before I did the break:
> 
>   y,j = nil
>   myobj.each do |x,i|
>    #...
>    if some_condition
>      y,j = x,i
>      break
>    end
>    #...
>   end
> 
>   last_obj, last_index = y,j
> 
> Two more variables and much ugliness. No, thanks.

One more reason to use ':' to indicate local, so the former code runs
unchanged.

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