Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Method-Function Equivalence

Method-Function Equivalence

Learn the different ways to call a function in Perl.

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Perl’s object system is deliberately minimal. A class is a package, and Perl doesn’t distinguish between a function and a method stored in a package. The same built-in, sub, declares both. Perl will happily dispatch to a function called as a method. Likewise, we can invoke a method as if it were a function—fully qualified, exported, or as a reference—if we pass in our own invocant manually.

Invoking the wrong thing in the wrong way causes problems.

Caller side

Consider a class with several methods:

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package Order {
    use List::Util 'sum';
    
    sub calculate_price {
        my $self = shift;
        return sum( 0, $self->get_items );
    }
    ...
}

Given an Order object $o, ...