Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Anonymous Functions

Anonymous Functions

Learn about anonymous functions in Perl.

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An anonymous function is a function without a name. It behaves exactly like a named function—we can invoke it, pass it arguments, return values from it, and take references to it. Yet, we can access an anonymous function only by reference, not by name.

A Perl idiom known as a dispatch table uses hashes to associate input with behavior:

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my %dispatch = (
    plus => \&add_two_numbers,
    minus => \&subtract_two_numbers,
    times => \&multiply_two_numbers,
);
sub add_two_numbers { $_[0] + $_[1] }
sub subtract_two_numbers { $_[0] - $_[1] }
sub multiply_two_numbers { $_[0] * $_[1] }
sub dispatch {
    my ($left, $op, $right) = @_;
    return unless exists $dispatch{ $op };
    
    return $dispatch{ $op }->( $left, $right );
}
 
 say dispatch(3,'times',2);
 say dispatch(3,'plus',2);
 say dispatch(3,'minus',2);

The dispatch() function takes arguments of the form (2, 'times', 2), evaluates the operation, and returns the result. A trivial calculator application could use dispatch to figure out which calculation to perform based on user input.

Declaring anonymous functions

The sub built-in used without a name creates and returns an anonymous function. We should ...