From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-10-04T17:28:48+09:00
Subject: Re: Specifying local and external block parameters (that old chestnut)

On Fri, Oct 04, 2002 at 04:44:17PM +0900, Gavin Sinclair wrote:
> From: "Mauricio Fern�ndez" <batsman.geo@yahoo.com>
> 
> 
> > > 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
> >
> > I hereby claim authorship of any syntax derived from the use of
> > the ':' prefix to indicate the scope of block parameters, based on
> > [ruby-talk:52401]. All rights reserved.
> >
> > :-)
> 
> Fair enough.  Your royalty cheque is in the mail.

Great! The first time in my life I do earn my very own money! Hehe.

> > > or
> > >
> > >   collection.each do |a,b,c|
> > >     external b
> > >     ...
> > >   end
> > >
> > > I'm not sure which of the above I prefer.  One should optimize for the
> common
> > > case.
> >
> > I'd head towards ':'. Reason: less typing.
> > Plus we're used to having '@' and '@@' to indicate scope (kinda), so it
> > just makes sense for me.
> 
> Exactly.
> 
> > Local params would surely be more common, but marking them with ':'
> > instead of the external ones has the additional advantage of not
> > breaking any code out there.
> 
> I disagree.  Marking the external ones rather than internal ones is SO much
> more sensible.  Seeing a.each do |:x| everywhere is too ugly.  Changes have
> been made that break code before.  How much code would it really break anyway?

I do agree with you, really. I makes more sense to mark external.
As I'm quite new to Ruby I thought backwards-incompatible changes would
be avoided like plague; but if that's not much of a concern then it'd
definitively be better to use ':' for locals.

> > The transition could be made very easy if
> > the current scoping rules are mixed with ':' for a while.
> >
> > So in
> >    blabla.aaaa do |a,:b|
> >
> >    end
> >
> > a is local if there's no variable named 'a' previously defined,
> > otherwise external
> 
> This sort of confusion is exactly what we want to get away from.

During the transition a warning could be issued so ':' is added where
needed.

> > b is local even if there's already 'b' in the external scope
> >
> > bottom line: nothing breaks, ':' forces local
> >
> > Ruby can issue a warning iff there was no 'a' variable before, as this
> > code would break once the old scoping rules are thrown away and only the
> > presence or absence of ':' is significant.

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