From: Dennis Decker Jensen <dennisdecker@...>
Date: 2001-03-13T03:26:02+09:00
Subject: [ruby-talk:12521] SV:  Re: FEATURE REQUEST: 'my' local variables

Mark Slagell wrote:
> Still... this One Particular Behavior gets brought up by a pretty
> significant portion of new ruby users who are confused or bothered by
> it.  It's the one real "fix" I really would like to see incorporated if
> an agreeable (and hopefully fully backwards-compatible) syntax can be
> settled on.

Agreed. I didn't like the notion of 'my' but a more explicit notion would be
beneficial. I find this very hard but will try anyway...:

As far as I can see, there are currently two main suggestions:

a) addition of another kind of block-scope
b) addition of another variable-prefix for block-local variables

...And actually a third suggestion (c) but it seems to move towards the
second suggestion (b).

Ad a)
-----
This was one of the first things in Ruby to confuse me until I read about
the different precedences of binding (do...end vs. {...}, and vs. &&, etc.)

What about prefixing do...end and {...} with the keyword "local"?
Like this:

z = 7; puts z # -> 7
[1, 2, 3].each local { |x, y, z| y=x*3; z=y*2; p z } # -> 6 12 18
puts z # -> 7
puts y # -> [NameError] y not initialized

# y is strictly local and not accessible after end of block-scope
# z is strictly local like y
#	but with access to surrounding scope like usual
# x is like usual

The position determines it. If each was reimplented to yield two arguments
to the block, y would also become an usual local like x. When used with
do...end (local do ... end), all of the locals would be visible afterwards
(x, y and z), but z would still not be "hurt" and preserve its previous
value which in this case is 7.

Ad b)
-----

loop { |a, b, c, :d, :c| ... }

I don't like this, since they remind me of symbols and not of strictly local
variables...

loop { |a, b, c, ::d, ::c| ... ::d = ::d + 1; ... }

It looks akward, but only because the syntax is new to Ruby. Unlike my
suggestion earlier, no position determines which variables are strictly
local. This I like! The concept is explicit and clear. But i would like a
more readable syntax instead of something obscured. "::" reminds me of
Perl-syntax a bit too much...

Is "!" taken? ;-) I could also imagine
loop { |a, b, c, !d, !c| ... !d = !d + 1; ... } # ;-) a lot of NOTs...

However. The main question remains: Is the new syntax worth the added
complexity? Maybe some other syntax?....

BTW: I haven't got a clue about the implementation and the rest, so thanks
to Matz for keeping all of us straight on the road... :-)

Dennis