1. You're assigning to a method call at: my $self->pop = shift;. You don't want to do that (though it's in some cases possible to make it work). You want to assign to the internal property "pop" instead.

2. The "my" in that statement is throwing off the perl interpreter. my should only be used to introduce new variables. Object properties aren't new variables, so lose it.

Corrected example for pop():

sub pop{
    my $self = shift;
    if (@_) { # test for next argument
      $self->{pop} = shift;  # assign argument to "pop" value
    }
    return $self->{pop};     # return "pop" value
}
[download]

Note that pop is also a built-in function, so overriding it in your packages may lead to confusion or worse.

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