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Postings from January 2017
On 30 January 2017 at 18:13, Dave Mitchell <davem@iabyn.com> wrote:
> On Sat, Jan 28, 2017 at 03:31:48PM +0100, demerphq wrote:
>> My experience with locked hashes is that as currently implemented they
>> are nearly useless.
>
> Their main advantage (as exposed by 'use fields') is that they check,
> at *compile* time, that you're not using an invalid key for an
> object, which has always been a big elephant in the room as regards
> Perl's idiosyncratic use of hashes as objects.
>
> package Foo;
>
> use fields qw(a b c);
>
> sub new { bless { qw(a 1 b 2 c 3) } }
>
> package main;
>
> my Foo $Fr = Foo->new();
>
> $Fr->{a} = 1; # ok
> $Fr->{d} = 1; # compile-time error
>
> I'm not sure what checking is done at run time.
As far as I can tell none of the behavior demonstrated by your code is
implemented by restricted hashes; in fact your sub new{} overrode the
use of Hash::Util::lock_keys() in the constructor in fields.pm so your
code does not use restricted hashes at all.
An actual exception from restricted hash code would look like this:
use Hash::Util qw(lock_hash);
my %hash=(foo=>1,bar=>2);
lock_hash(%hash);
print $hash{blah};
__END__
Attempt to access disallowed key 'blah' in a restricted hash at ....
FWIW, I don't think I have ever seen anyone write
my Foo $foo= Foo->new();
in the wild. No doubt they do somewhere, but not in any code I have
looked at. And if you omit the "Foo" from "my Foo" (an easy mistake
IMO) then the compile time checks go away as well, and fields.pm
becomes completely run-time.
cheers
Yves
Yves
ps: Where can i read up on how this is working at an internals level?
--
perl -Mre=debug -e "/just|another|perl|hacker/"
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