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Postings from November 2021
On Wed, Nov 10, 2021 at 1:59 PM Ovid via perl5-porters <
perl5-porters@perl.org> wrote:
> Hi Porters!
>
> I would love to see a permanent keyword for Perl. It initializes a
> variable once and only once. It would look like this:
>
> #!/usr/bin/env perl
>
> use 5.38.0;
> use warnings;
>
> sub variables {
> my $name = shift;
> return sub {
> my $my = 1;
> state $state = 1;
> permanent $permanent = 1;
> say "$name: my is $my. state is $state. permanent is
> $permanent";
> $_++ for $my, $state, $permanent;
> }
> }
>
> my $first = variables('first');
> my $second = variables('name');
>
> say "First";
> $first->();
> $first->();
> $first->();
>
> say "Second";
> $second->();
> $second->();
> $second->();
>
> And the output would be:
>
> First
> first: my is 1. state is 1. permanent is 1
> first: my is 1. state is 2. permanent is 2
> first: my is 1. state is 3. permanent is 3
> Second
> name: my is 1. state is 1. permanent is 4
> name: my is 1. state is 2. permanent is 5
> name: my is 1. state is 3. permanent is 6
>
>
> Currently, state's documentation says this:
>
> "state" declares a lexically scoped variable,
> just like "my". However, those variables will
> never be reinitialized, contrary to lexical
> variables that are reinitialized each time their
> enclosing block is entered. See "Persistent
> Private Variables" in perlsub for details.
>
> But that's not quite correct. It's never reinitialized unless the scope is
> dynamic, in which case it is.
>
> Permanent variables would *never* be reinitialized. Not only will this be
> more clear to existing Perl developers, it might help new Perl developers
> who misuse state variables. It might also clear up future issues with
> Corinna, but I won't go there now :)
>
This is a bit confusing. The scope you created is not any more dynamic than
any other - you are creating a different subroutine with its own pad. I
think if you want a variable to be permanent through multiple pads, that's
what the package stash is for.
-Dan
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