> Hi all, I'm having a look in to object oriented perl. Can anyone tell me
> what the difference between @_ and shift is?
One is a variable, one is function/operator ;-)....
As far as I know there is no
> difference except "shift" removes the parameter from the @_ array so
if you
> were to "shift" all parameters passed to a function nothing would be
> containted in @_ is this correct?
>
@_ is just a special Perl variable, it so happens that it is what is
used to store the arguments to a subroutine temporarily (it has other
uses, see perldoc perlvar). It also happens that the first argument to
a subroutine acting like a method is always the object/class that the
method is invoked on. C<shift> is just a function that removes the
first/top element of an array, any array, in OOP or not.
This happens to make things very convenient, aka in most methods you
will want to remove the instance/class from the argument list to get the
actual argument list back, and shift by itself will default to use @_.
So essentially you are left with some syntactic sugar to make life easier.
So,
my $self = shift;
Just says to grab the instance from @_ (by default), store it in $self,
and restore the arg list to what the user actually passed. You don't
*have* to do it, but it is very convenient.
> I'm asking because I'm a little confused about using it. Why can't I do
> this:
>
> #######################################
> sub nickname {
> my $self = shift;
> return $self->{NICK};
> }
No reason you can't. Provided you have already set $self->{NICK} or
don't mind getting an undefined value.
> #######################################
>
> But I can do this:
>
> #######################################
> sub nickname {
> my $self = shift;
> if (@_) { $self->{NICK} = shift
> }
> return $self->{NICK};
> }
> #######################################
>
Only difference here is that you set $self->{NICK} in the event that an
argument was passed, aka after shift'ing there is still an argument in
@_ (namely the value you want to set NICK to).
Additional suggested reading:
perldoc perlboot
perldoc perltoot
perldoc perltooc
http://danconia.org
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