Hi,
Juerd wrote:
> Will Perl 6 support mutable for-reverse?
I'd like it! :)
> Some possible answers that I could think of:
>
> (a) Yes, but as a special case
> (b) Yes, because reverse returns lvalue aliases
> (c) No
>
> But there's another one, that I didn't immediately think of:
>
> (d) Yes, because reverse @foo always behaves like an array (rather
> than a function that *returns* a list), just with a different view:
> the elements are in the wrong order.
Where is the difference (for the user) between a subroutine which
returns an appropriate proxy object and an array?
# Perl 5
sub foo {...}
foo[42]; # really foo([42])
# Perl 6
sub foo {...}
foo[42]; # really (foo())[42]
foo{"Pugs"}; # really (foo()){"Pugs"}
foo<Pugs>; # really (foo()){"Pugs"}
> This option d is interesting, and would probably be nice to have,
> because it would also allow this (contrived and useless) kind of
> thing:
>
> push reverse(@foo), $bar;
>
> And while that isn't very interesting, I think something like
>
> my @bar := reverse @foo;
>
> would be very useful.
Yep :)
(Also note that if we make &reverse return an appropriate proxy object
so this example works, for reverse @array {...} will automatically be
optimized.)
> The same thing would be interesting for zip:
>
> my @xyzzy := @foo Y @bar;
>
> Assuming this results in an even number of elements in @xyzzy, pushing
> a single element onto @xyzzy could result in an element added to @foo
> every odd, and to @bar every even time.
>
> Would something like that be possible? Wanted?
I'd like that as well. (Generally, I'd like to see many lvalue subs and
methods in default Perl 6.)
> Not too costly?
I think it'd even optimize many cases:
for @foo ¥ @bar {...}
# Generating a new array containing @foo ¥ @bar is, thanks to
# zip's laziness, unnecessary.
(BTW, IIUC, per r6622 of S06.pod [1] &zip returns an array of arrayrefs
now:
for zip('a'...; 0...; @foo) -> [$a, $i, $x] { ...}
(Or does for no longer automatically take as much elements from the
input array as needed? I.e. does
my @array = <a b c d>;
for @array -> $a, $b { say "$a $b" }
no longer output "a b\nc d\n", but die?))
--Ingo
[1] http://svn.perl.org/perl6/doc/trunk/design/syn/S06.pod
--Ingo
