Re: Method invocation arrow (LPORM)
Jan == Jan Eden [EMAIL PROTECTED] writes: Jan Yes, SUPER:: is introduced just two paragraphs later. I read on, but the uncertainty about $class-Animal::speak kept bugging me. ;) Thank you for the feedback. I'll note that for a future edition of the book. That's also very similar to the way I have it in perlboot, but nobody noted it there yet. :( -- Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095 [EMAIL PROTECTED] URL:http://www.stonehenge.com/merlyn/ Perl/Unix/security consulting, Technical writing, Comedy, etc. etc. See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training! -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Method invocation arrow (LPORM)
On Feb 9, Randal L. Schwartz said: Jan == Jan Eden [EMAIL PROTECTED] writes: Jan Yes, SUPER:: is introduced just two paragraphs later. I read on, but the uncertainty about $class-Animal::speak kept bugging me. ;) Thank you for the feedback. I'll note that for a future edition of the book. That's also very similar to the way I have it in perlboot, but nobody noted it there yet. :( I would have, but I didn't think it necessary. When the question was asked, I went to the perlboot doc since I figured that was where the chapter originated. -- 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. ] -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Method invocation arrow (LPORM)
On 2/7/2004 1:23 PM, James Edward Gray II wrote:
On Feb 7, 2004, at 10:02 AM, Jeff 'japhy' Pinyan wrote:
On Feb 7, Jan Eden said:
{ 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.
I was going to ask this too. I'm glad I finished reading the email.
I'm not familiar with the book though, so I will ask this? Does it
eventually go on to introduce SUPER::? That's what I would prefer here
and I just want to make sure you're aware of the option.
Hmm, I think a good exercise would be to write code snippets to
demonstrate the differences between the four method calls:
Package::method()
$class-method()
$class-Package::method()
$class-SUPER::method()
or five if you count:
method Package ...
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Re: Method invocation arrow (LPORM)
On Feb 8, 2004, at 6:51 AM, Randy W. Sims wrote: Hmm, I think a good exercise would be to write code snippets to demonstrate the differences between the four method calls: Package::method() Is this really a method call? I think of it as a package qualified subroutine call. $class-method() $class-Package::method() $class-SUPER::method() This one should only be used inside an overriden method, I think. or five if you count: method Package ... Let's not. laughs James -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Method invocation arrow (LPORM)
Hi all,
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.
He gives the following example for overriding methods:
{ package Mouse
@ISA = qw{Animal};
...
sub speak {
my $class = shift;
...
Animal::speak($class);
...
}
}
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.
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);
And when Perl does not find Animal::speak in Mouse, to:
Animal::Animal::speak(Mouse;
and to higher classes if speak is not found there. Now my question:
Does Perl reduce Animal::Animal::speak(Mouse) automatically to
Animal::speak(Mouse). And, if speak is not in Animal, how does it handle an
expression like:
LivingCreature::Animal::speak(Mouse);
It seems to me that the hard-coded package name we got rid of by using method calls
just got back into our syntax. At the same time, I am sure the code works (have not
tried it yet) and Perl does as it should.
But how does this work?
Thanks for any explanations,
Jan
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Re: Method invocation arrow (LPORM)
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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Re: Method invocation arrow (LPORM)
Jeff 'japhy' Pinyan wrote: 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. I see. So Animal just marks the starting point for the search, and it might become LivingCreature::speak($class) later on if speak is not found in Animal. 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. That's exactly the information I was looking for. Thank you, Japhy. - Jan -- These are my principles and if you don't like them... well, I have others. - Groucho Marx -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Method invocation arrow (LPORM)
On Feb 7, 2004, at 10:02 AM, Jeff 'japhy' Pinyan wrote:
On Feb 7, Jan Eden said:
{ 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.
I was going to ask this too. I'm glad I finished reading the email.
I'm not familiar with the book though, so I will ask this? Does it
eventually go on to introduce SUPER::? That's what I would prefer here
and I just want to make sure you're aware of the option.
James
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Re: Method invocation arrow (LPORM)
James Edward Gray II wrote:
On Feb 7, 2004, at 10:02 AM, Jeff 'japhy' Pinyan wrote:
On Feb 7, Jan Eden said:
{ 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.
I was going to ask this too. I'm glad I finished reading the email.
I'm not familiar with the book though, so I will ask this? Does it
eventually go on to introduce SUPER::? That's what I would prefer here
and I just want to make sure you're aware of the option.
Yes, SUPER:: is introduced just two paragraphs later. I read on, but the uncertainty
about $class-Animal::speak kept bugging me. ;)
- Jan
--
These are my principles and if you don't like them... well, I have others. - Groucho
Marx
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Re: Method invocation arrow (LPORM)
James Edward Gray II wrote:
On Feb 7, 2004, at 10:02 AM, Jeff 'japhy' Pinyan wrote:
On Feb 7, Jan Eden said:
{ 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.
I was going to ask this too. I'm glad I finished reading the email.
I'm not familiar with the book though, so I will ask this? Does it
eventually go on to introduce SUPER::? That's what I would prefer here
and I just want to make sure you're aware of the option.
Yes, SUPER:: is introduced just two paragraphs later. I read on, but the uncertainty
about $class-Animal::speak kept bugging me. ;)
- Jan
--
These are my principles and if you don't like them... well, I have others. - Groucho
Marx
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Re: Method invocation arrow (LPORM)
On Feb 7, 2004, at 2:20 PM, Jan Eden wrote: Yes, SUPER:: is introduced just two paragraphs later. I read on, but the uncertainty about $class-Animal::speak kept bugging me. ;) Excellent. I figured that was the case, but I was just making sure. James -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
