Perl Function in a Hash

Perl Function Explained – Part 5

Perl Course

Foreword: In this part of the series I explain how to make a Perl function an element of a hash.

By: Chrysanthus Date Published: 8 Sep 2015

Introduction

This is part 4 of my series, Perl Function Explained. In this part of the series I explain how to make a Perl function an element of a hash. To make a function an element of a hash, use the anonymous function scheme. You should have read the previous parts of the series before coming here, as this is a continuation.

The Anonymous Function Scheme
This scheme does not use a name to define a function; the function is anonymous. An example of its coding is:

use strict;

    my $coderef = sub
            {
                #statements
                print "seen";
            };

    &$coderef();

An anonymous function definition ends with a semicolon. However, in a hash, you omit the semicolon.

Hash by Parentheses
The following is a hash created using the hash parentheses and a function is an element of the hash:

use strict;

    my %ha = (
             apple=>"purple",
             coderef=>sub {
                            #statements
                            print "seen";
                        },
             banana=>"yellow"
             );

    &{$ha{coderef}};

In the hash, the elements are separated by commas. So, the function body is separated from the next element by a comma (not a semicolon). In the hash, $ha{coderef} holds the code reference. Note how the function call reference, $ha{coderef} has been dereferenced by placing it inside &{ }.

The function can have arguments as in the following code:

use strict;

    my %ha = (
             apple=>"purple",
             coderef=>sub {
                            #stateents
                            print $_[0];
                        },
             banana=>"yellow"
             );

    &{$ha{coderef}}("seen");

Note that in the function call, the list of argument(s) are placed after the dereferenced code (not inside).

Hash by Assignment
The first code above can be replaced by the following:

use strict;

    my %ha;

    $ha{apple} = "purple";
    $ha{coderef} = sub {
                            #statements
                            print "seen";
                        };
    $ha{banana} = "yellow";

    &{$ha{coderef}};

Inside the hash you use =>. Outside, you use =. Any assignment statement (anonymous function) ends with a semicolon.

The code above where the function has an argument, can be replaced by the following:

use strict;

    my %ha;

    $ha{apple} = "purple";
    $ha{coderef} = sub {
                            #statements
                            print $_[0];
                        };
    $ha{banana} = "yellow";

    &{$ha{coderef}}("seen");

You can have more than one subroutine (function) in a hash.

That is it for this part of the series.

Chrys

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