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Postings from November 2021
On Wed, Nov 10, 2021 at 2:23 PM Dan Book <grinnz@gmail.com> wrote:
> 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.
>
Or a state variable initialized in the scope containing the closure.
-Dan
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