Re: [perl #131599] [RFC] Allow a Callable for `is default` that will generate default values
FWIW, with:
http://modules.perl6.org/dist/Hash::Restricted:cpan:ELIZABETH
one can restrict access to a hash to a certain set of keys:
use Hash::Restricted;
my %h is restricted = a => 42, b => 666; # restrict to keys at initialization
my %h is restricted; # restrict to keys a, b, c
> On 18 Jul 2018, at 17:32, Alastair Douglas via RT
> wrote:
>
> On Mon, 19 Jun 2017 09:30:41 -0700, brad wrote:
>> The way Moose in Perl 5 works around this is to give it a subroutine
>
>> there currently isn't as far as I know, a way to do what you intended.
>
> I'd like this feature as well. I was in IRC asking about whether we could
> restrict a hash in the same way python does, such that %hash
> dies.
>
> It was noted that one can do
>
> my %h is default(Failure.new);
>
> This would put a Failure in anything that didn't exist, which would detonate
> whenever accessed. Presumably, this would be the same Failure each time, but
> that's probably OK.
>
> It means there is no way of generating a default based on access. I think
> that would look something like:
>
> my %h is default(-> $key { Failure.new("$key not provided") });
>
> But then how would it know to run the Callable to generate the default,
> rather than simply providing the Callable as the default? I have no answer
> for that.
Re: [perl #131599] [RFC] Allow a Callable for `is default` that will generate default values
FWIW, with:
http://modules.perl6.org/dist/Hash::Restricted:cpan:ELIZABETH
one can restrict access to a hash to a certain set of keys:
use Hash::Restricted;
my %h is restricted = a => 42, b => 666; # restrict to keys at initialization
my %h is restricted; # restrict to keys a, b, c
> On 18 Jul 2018, at 17:32, Alastair Douglas via RT
> wrote:
>
> On Mon, 19 Jun 2017 09:30:41 -0700, brad wrote:
>> The way Moose in Perl 5 works around this is to give it a subroutine
>
>> there currently isn't as far as I know, a way to do what you intended.
>
> I'd like this feature as well. I was in IRC asking about whether we could
> restrict a hash in the same way python does, such that %hash
> dies.
>
> It was noted that one can do
>
> my %h is default(Failure.new);
>
> This would put a Failure in anything that didn't exist, which would detonate
> whenever accessed. Presumably, this would be the same Failure each time, but
> that's probably OK.
>
> It means there is no way of generating a default based on access. I think
> that would look something like:
>
> my %h is default(-> $key { Failure.new("$key not provided") });
>
> But then how would it know to run the Callable to generate the default,
> rather than simply providing the Callable as the default? I have no answer
> for that.
[perl #131599] [RFC] Allow a Callable for `is default` that will generate default values
On Mon, 19 Jun 2017 09:30:41 -0700, brad wrote:
> The way Moose in Perl 5 works around this is to give it a subroutine
> there currently isn't as far as I know, a way to do what you intended.
I'd like this feature as well. I was in IRC asking about whether we could
restrict a hash in the same way python does, such that %hash
dies.
It was noted that one can do
my %h is default(Failure.new);
This would put a Failure in anything that didn't exist, which would detonate
whenever accessed. Presumably, this would be the same Failure each time, but
that's probably OK.
It means there is no way of generating a default based on access. I think that
would look something like:
my %h is default(-> $key { Failure.new("$key not provided") });
But then how would it know to run the Callable to generate the default, rather
than simply providing the Callable as the default? I have no answer for that.
