Forwarded Message From:"christopher j bottaro"
<[EMAIL PROTECTED]>Reply-to:[EMAIL PROTECTED]:[EMAIL PROTECTED]:help with
classes...Date:Tue, 10 Dec 2002 04:45:15 -0600MIME-Version:1.0Content-Type:text/plain;
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hey,i'm a c/c++ programmer struggling to pick up OO perl. i've been reading the
perltoot and i have question about the following:package Person; use strict; sub
new { my $self = {}; $self->{NAME} = undef; $self->{AGE} =
undef; $self->{PEERS} = []; bless($self); # but see below
return $self; } sub name { my $self = shift; if (@_) {
$self->{NAME} = shift } return $self->{NAME}; }ok, in the sub new(), i
understand that $self is a ref and new() is returning it. what does bless do (the
single arg version). i thought bless takes 2 args: what to bless and the name to
bless it with...? what else does bless do besides give something a type?in the sub
name(), what is the first argument? obviously its a reference to a person object (or
whatever new() returned). but why? i've written subs before and used shift(), but
this is confusing me. say i have $person = Person->new(); now i do $person->name();
i'm not passing it any arguments so why is the sub name() receiving an argument which
is a reference to a Person object? does it have something to do with bless()?
something to do with being a part of package?thanks for the help....=)christopher
Hi Chris,
I felt the same way when I first started out with classes, but keep at it,
it's not as hard as it looks :)
The single argument form of bless blesses the reference
into the current package. So if you have :
package Person;
my $ref=\%hash;
bless($ref);
$ref will be blessed into the Person package.
Once you have blessed a reference into a package, whenever you call a
method(sub) via that reference, the first argument perl passes
to that method is the reference. This happens behind the scenes
so when you call $ref->subname() and $ref is in the Person
package, perl substitutes that statement for
Person::subname($ref);
so $ref->destroy('Ring'); when $ref is in the Lotr package
ends up as Lotr::destroy($ref,'Ring');
So in order to get to the other args, you do
a shift to remove the ref from the @_ array.
Hope that's been of help.
Cheers.
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