Twigil exclamation mark !

[yuki-kimoto]

I think twigil exclamation mark ! is a little difficult to read.

In Perl, ! mean "deny". And ! is often used.

if (!$!title) {

}

What about other mark?

if (!$:title) {

}

[stevan]

We are following what Perl 6 does here. Also I don't think that $:foo could be a valid twigil.

[yuki-kimoto]

p5-mop is Perl5 project, not Perl6. I don't understand the meaning that "We are following what Perl 6 does here".

[stevan]

Yuki - the idea is to keep as much compatibility with Perl 6 as possible.

[yuki-kimoto]

OK.

By the way, Dose twigil work well in Perl5? For example, Dose the following code work well?

"$!title"

$! is special variable. How to distinguish these cases?

[stevan]

Right now the twigil module is a bit of a hack with the parser, it basically finds $! and then looks ahead to see if there is a bareword after it, if there is, it interprets it as a twigil. If it becomes part of the core, then it will most certainly become a proper part of the parser.

[yuki-kimoto]

If it don't work in lexical scope, backward compatible is broken. The change maybe denied from core team. Can twigil work in only lexical scope?

[stevan]

Yes, it works in lexical scope (as well as our and state scope). If the change is denied by the core team we will go back to regular variables ($foo as opposed to $!foo).

[yuki-kimoto]

If attribute foo is private variable, we can also use the name $_foo to prevent crash variable names. If attribute name crash lexical variable, we can use accessor.

has $x is rw;
has $_y;
method foo {

   my $x;
   my $y;
   if ($x eq $self->x) {

   }

    if ($_y eq $y) {

    }
}

I think even if twigil is denied, mop don't have big trouble. And you can also think twigil as next step of mop.

[stevan]

Yes, these are the techniques I used when I ported Plack, but honestly they are not nearly as nice as the twigil.