On Feb 7, Jan Eden said:
>I just work my way through "Learning Perl Objects, References & Modules".
>Now at one point, I am stuck: Randal introduces classes and methods in
>Chapter 8.
Hopefully I'll answer before Randal. ;)
>{ package Mouse
> @ISA = qw{Animal};
> ...
> sub speak {
> my $class = shift;
> ...
> Animal::speak($class);
> ...
> }
>}
I was about to ask why it's written this way, but upon checking the
source, I see that this is the way the first example on overriding a
method looks.
>Since there is a method speak in Mouse, it would override the parent's
>classes method Animal::speak if the latter were not called explicitly.
>
>But, as Randal points out, this forces Perl to look for speak in Animal
>and nowhere else - without the method invocation arrow, it cannot check
>@ISA for ancestor classes.
Right. I was about to say "why is it written this way?" but then I saw
the rest of the examples (and read the rest of your email).
>So far, I get the point. But then he introduces the following solution:
>
>$class->Animal::speak(@_);
>
>Apart from the fact that @_ should be unnecessary here (or did I get
>something wrong), this should expand to:
>
>Mouse::Animal::speak("Mouse");
No, it does not. If $class is 'Mouse', then
$class->method(@_);
will try looking for Mouse::method(), and if not, it will look through
Mouse's @ISA for a class that DOES supply method(). BUT HERE, we're using
$class->OtherClass::method(@_);
which says explicitly to start looking for method() in OtherClass (and if
it fails there, look in OtherClass's @ISA). So
$class->Animal::speak();
in your case becomes
Animal::speak($class);
except that it becomes that DYNAMICALLY.
>And when Perl does not find Animal::speak in Mouse, to:
Ah, here's the confusion. This isn't looking for a method named
'Animal::speak' in 'Mouse'; it's looking for a method named 'speak' in
'Animal'.
Only the right-most part of a Thing::Like::this denotes the name of a
method.
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]
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