Reference to an Anonymous Subroutine in Perl

Perl References Optimized – Part 5

Perl Course

Foreword: In this part of the series, we look at Perl Reference to an anonymous subroutine (function).

By: Chrysanthus Date Published: 10 Jul 2015

Introduction

This is part 5 of the series, Perl References Optimized. In this part of the series, we look at Perl Reference to an anonymous subroutine (function). In Perl, a function is called a subroutine, abbreviated, sub. Anonymous means, no name. You should have read the previous parts of the series before reaching here, as this is a continuation.

Named and Anonymous Subroutine
Anonymous means, no name. A named subroutine is defined as follows:

sub subName
    {
        #statements
    }

where subName is the name of the subroutine (function). An anonymous subroutine is defined as follows:

sub
    {
        #statements
    }

As you can see there is no name for this subroutine. A subroutine should be identified. Instead of having a name, you can have a reference that refers (points) to it. You do this as follows:

$coderef = sub
                    {
                        #statements
                    };

Here you have a statement and so note the semicolon just after the closing brace, }. $coderef is a scalar that holds a reference to the subroutine (region) in memory.

Note: sub{} is an operator that returns a reference.

Calling a Subroutine using its Reference
You call a subroutine using its reference as follows:

    &$coderef;

or

    &$coderef(argument list);

You begin with & and then the scalar variable that holds the reference. The first statement above is used when there is no argument; the second statement is used when there are arguments. The first statement can still be “&$coderef();” with empty parentheses.

Illustration
Read and try the following code where no argument is sent:

use strict;

my $cref = sub
            {
                print "seen";
            };

&$cref;

The output of this program is “seen”. Read and try the following code, where three arguments are sent:

use strict;

my $cref = sub
            {
                print $_[0] . "\n";
                print $_[1] . "\n";
                print $_[2] . "\n";
            };

&$cref("aaa", "bbb", "ccc");

The output of this program are the three arguments in three lines.

Returning
A function (subroutine) as the ones above can return a value or a reference, depending on what it does. The following code shows how to handle whatever is returned.

use strict;

my $cref = sub
            {
             return "seen";
            };

my $ret = &$cref;
print $ret;

That is: as you call the function with &, just assign what is returned to a variable.

We end here for this part of the series.

Chrys

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