Re: [PATCH] Git.pm: do not break inheritance
- From
- Christian Jaeger <christian@jaeger.mine.nu>
- Date
- Oct 18, 2008, 22:21 UTC
- Message-ID
- <48FA6152.6020006@jaeger.mine.nu>
- In-Reply-To
- <7vabd1aaqx.fsf@gitster.siamese.dyndns.org>
Junio C Hamano wrote:
Show 16 quoted lines
> That's how you would write class methods, isn't it? IOW, your callers
> can say:
>
> my $self = new Git();
> $self->method(qw(a b c));
> Git::method(qw(a b c))
>
> and you can start your method like this:
>
> sub method {
> my ($self, @args) = _maybe_self(@_)
> ...
> }
>
> and use @args the same way for either form of the call in the
> implementation. I see, a magic way to offer both an OO and procedural api. Well, partial procedural api, since not all of the methods can work without the $self.
Show 16 quoted lines
> Two obvious pitfalls are:
>
> - You cannot use $self if you set up your parameters with _maybe_self;
>
> - The second form of the call would call directly into Git::method, never
> your subclasses implementation, even if you write:
>
> use Git;
> package CJGit;
> our @ISA = qw(Git);
>
> sub method {
> ...
> }
>
> (This is no problem iff people are calling procedures in object notation if they actually have got an object at hands. I.e. if you've got some code which does:
my $repo= Git->repository(...); $repo->foo;
then all is fine, and I would think it would be weird if people called Git::foo($repo, ... ) in such a case. Well for my purposes it's not a problem anyway, since if a user wants to use the extensions, he needs to actually do this:
my $repo= CJGit->repository(...);
and then it should be clear that one shouldn't call Git:: directly. The problem will only be in cases where an extended object is being fed to existing code which calls Git:: with objects in the hope that virtual method calls are going to the extended class; well, let's fix those bad call sites when they are being discovered... Maybe this warrants a warning somewhere.)
Show 13 quoted lines
>> sub _maybe_self {
>> - # This breaks inheritance. Oh well.
>> - ref $_[0] eq 'Git' ? @_ : (undef, @_);
>> + UNIVERSAL::isa($_[0], 'Git') ? @_ : (undef, @_);
>> }
>>
>> # Check if the command id is something reasonable.
>>
>
> The patch looks Ok, as long as you have a working UNIVERSAL::isa() in your
> version of Perl. My reading of perl561delta,pod says that Perl 5.6.1 and
> later should have a working implementation.
> From http://perldoc.perl.org/perl561delta.html:
Show 5 quoted lines
> UNIVERSAL::isa() > > A bug in the caching mechanism used by UNIVERSAL::isa() that affected > base.pm has been fixed. The bug has existed since the 5.005 releases, > but wasn't tickled by base.pm in those releases.
This looks like only a bug in some (corner?) cases; I've verified that I've been using the isa() method *or* function since perl 5.005_03, and haven't had issues with it. I can't easily verify though when I switched from
#if (Scalar::Util::blessed($value) and $value->isa("Eile::Html")) { to if (UNIVERSAL::isa($value,"Eile::Html")) {
(because it was simpler to write, once I discovered that I could just call the function directly instead of relying on method dispatch) but that might not have made a difference.
Christian.