CODEWITHSUNDEEP
perl
Herdsman
Herdsman

Reputation: 859

Difference between double colon and arrow in perl

If it is duplicate, say so. I Have not found it, only for PHP but for Perl. So If I can write full name of e.g. Class::sub() or $Class::scalar, I can write Class->sub or $Class->scalar(in case I have used or required the Class), what is the main difference in perl?

The problem is: Class Animal.pm:

#!/usr/bin/perl -w
package Animal;
our $VERSION = '0.01';
sub speak {
    my $class = shift;
    print "a $class goes ", $class->sound;
}
sub sound{
    die "You have to defined sound() in a subclass";
}

Then Class Horse.pm:

#!/usr/bin/perl -w
package Horse;
use Animal;
our @ISA = qw[Animal];
our $VERSION = '0.01';
sub sound { 'neight' }
1

And if I, in main program do this:

#!/usr/bin/perl -w
BEGIN{ unshift @INC, 'dirWithModules' }
 use Horse; use Animal;use Cow;
Animal::speak('Horse');

output---->"a Horse goes neight" BUT IF I OD 

#!/usr/bin/perl -w
BEGIN{ unshift @INC, 'dirWithModules' }
 use Horse; use Animal;use Cow;
Animal->speak('Horse')

output--->"You have to defined sound() in a subclass at Animal.pm"

So my question is, If I reference my method from class Horse.pm iherited sub speak from Animal.pm with ::, double colon, the NO PROBLEM - it will print the sound. However if I try to reference the sub with -> arrow, The $class is not inherited - that is, $class is Animal.pm itself, but not as parameter sent ('Horse'). So In what is :: and -> different?

Upvotes: 4

Views: 1303

Answers (1)

ikegami
ikegami

Reputation: 385655

Foo->bar() is a method call.

  • It will use inheritance if necessary.

  • It will pass the invocant (the left side of ->) as the first argument. As such, bar should be written as follows:

    # Class method (Foo->bar)
sub bar {
   my ($class, ...) = @_;
}

    or

    # Object method (my $foo = Foo->new; $foo->bar)
sub bar {
   my ($self, ...) = @_;
}

Foo::bar() is a sub call.

  • It won't use inheritance.

Upvotes: 6

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