What does "my ($self, %myInputs) = @_;" mean?

Question

I came across this line a lot of times in perl modules but I could not figure out what this exactly means.

my ($self, %myInputs) = @_;

Kindly explain me the statement so that I can proceed.

Perpetuity

Answer 1

Im guessing that is one of the first lines in a class method function. That line parses @_ which is the list of the function arguements, and extracts the first param which is always a reference to the object into $self and extracts the rest of them into a hash %myInputs. This ofcourse assumes that the function is called with the arguements in hash format, like in the below Perl/Tk function

$mw->Button(-text => "RIGHT", -command => sub { exit })
  ->pack(-side => 'right', -fill => 'both');

Realgar

Answer 2

my ($self, %myInputs) = @_;

Not all functions receive the first argument $self. In fact, by convention, only the ones invoked using the arrow operator do ->; invoking with -> implicitly sends a special argument referring to the object. All functions and methods in perl are declared the same way (using keyword sub). Only invocation determines whether or not the function is a method.

The my ($foo, $bar) = ( $x, $y ); is called parallel assignment. That's all that is going on here!

Observe a hash can be initialized from an array in Perl.

my @foo = qw/ foo bar baz quz /;
my %hash = @foo;
print $hash{foo}; # outputs bar

Because you're assigning to the hash %myInputs, the hash is explicitly assigned all inputs that are not the implicitly sent (because you're pulling that one off into $self). But be careful, it wouldn't make much sense to do the following right?

my @foo = qw/ foo bar baz /;
my %hash = @foo;
print $hash{baz} # what is this set too??

For the same reason, it also doesn't make much sense to invoke your function with an un-even amount of arguments! Both will generate a warning.

Despoil

But what is the need of using $self! It just confuses me so much! – Perpetuity

@Perpetuity $self refers to the object you're calling on. If you call my $a Animal->new, and then you call $a->run then $self (first argument) inside of sub run {} would be set to $a. In other languages you call it this. You can call it $this in Perl too if you're used to that, my $this = shift (though it's against convention). – Despoil

Answer 3

In Perl @_; is a Global Array Special Variables

Similar as @ARGV The array contain the command-line arguments intended for the script.

So in my ($self, %myInputs) = @_;

@_ would represent the argument of the Variable $ in the Hash-Variables %

Fierro