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Postings from September 2016
David Cantrell <david@cantrell.org.uk> writes:
> On Mon, Sep 26, 2016 at 10:32:11PM +0200, ?var Arnfj?r? Bjarmason wrote:
>
>> I've just pushed a smoke-me branch to remote UNIVERSAL::import from
>> that package, and make its (no)?import a fatal error via a hack to
>> gv.c: http://perl5.git.perl.org/perl.git/commitdiff/8804321d
>>
>> The motivation here is that someone doing "use UNIVERSAL;" in some
>> module shouldn't make $pkg->can("import") true for any value of $pkg
>> in your program.
>>
>> But technically this does break backwards compatibility without a
>> deprecation cycle. Because "use UNIVERSAL;" isn't an error today, and
>> some code on the CPAN redundantly uses that.
>
> You'll also break this:
>
> use UNIVERSAL;
> ...
> if(UNIVERSAL::isa($foo, 'Some::Class')) { ...
>
> which is a lot more convenient than checking to see if $foo is blessed,
> and if it is calling $foo->isa().
This continues to "work", and never required 'use UNIVERSAL', since the
function is provided by universal.c, not UNIVERSAL.pm.
> That said, it's not a particularly common idiom and I'm happy to change
> it in my code.
The idiom also breaks for any class that overrides isa, like
MooseX::Types::TypeDecorator and Moo::HandleMoose::FakeMetaClass, and is
warned against in the UNIVERSAL documentation:
https://metacpan.org/pod/UNIVERSAL#SYNOPSIS
# but never do this!
$is_io = UNIVERSAL::isa($fd, "IO::Handle");
$sub = UNIVERSAL::can($obj, "print");
https://metacpan.org/pod/UNIVERSAL#EXPORTS
Previous versions of this documentation suggested using isa as a
function to determine the type of a reference[.]
The problem is that this code would never call an overridden isa
method in any class
--
"I use RMS as a guide in the same way that a boat captain would use
a lighthouse. It's good to know where it is, but you generally
don't want to find yourself in the same spot." - Tollef Fog Heen
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