Toby Inkster > PerlX-ArraySkip > PerlX::ArraySkip

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NAME ^

PerlX::ArraySkip - sub { shift; @_ }

SYNOPSIS ^

        use PerlX::ArraySkip qw(skip);
        
        my @list = (
                'a',
                skip 'b',
                'c',
                skip 'd',
                'e',
        );
        
        print join '', @list;   # prints 'ace'

DESCRIPTION ^

The arrayskip function returns the entire list it was passed as arguments, except the first. This is an entirely trivial function and can be written as:

        sub arrayskip { shift; @_ }

The principle of TIMTOWTDI says that there are other ways of skipping the first item in an array, but according to my benchmarking this performs best.

A good question is: why would you want to do this? Well, in Perl there are two common function calling patterns, named parameters:

        give(
                giver     => $alice,
                recipient => $bob,
                gift      => $dinosaur,
        );

and positional parameters:

        give($alice, $bob, $dinosaur);

Positional parameters look fine when you've got one or two arguments, but can start looking unwieldly with four or more. Let's imagine that our give function takes a hypothetical fourth parameter, a boolean indicating whether the gift had wrapping paper on:

        give($alice, $bob, $dinosaur, 1);

When we come back to that line a few weeks, we might be confused about what it means. Is Bob giving Alice to the dinosaur once? The arrayskip function allows you to add extra items into the parameter list which will be skipped over, and can thus act as comments:

        give(
                arrayskip 'giver',     $alice,
                arrayskip 'recipient', $bob,
                arrayskip 'gift',      $dinosaur,
                arrayskip 'wrapped',   1,
        );

Now let's use a couple of tricks to make it even clearer. Firstly, PerlX::ArraySkip allows you to import the arrayskip function with your choice of name. You can call it something more suitable to your use case, such as arg. Secondly, the fat comma.

        use PerlX::ArraySkip 'arg';
        
        give(
                arg giver     => $alice,
                arg recipient => $bob,
                arg gift      => $dinosaur,
                arg wrapped   => 1,
        );

While the arguments are still positional (you can't change their order) they now have the appearance of named arguments, improving their readability, and the code's ease of maintenance.

So, why should you use PerlX::ArraySkip instead of defining your own arrayskip function? No reason at all. You can define your own function in fewer keystrokes than loading this module. Observe:

        use PerlX::ArraySkip 'skip';
        sub skip { shift; @_ }

This module, while it does provide an implementation, is mostly just a place to document the pattern. You could define your own function and include a reference to this module as a comment:

        sub arg { shift; @_ } # see PerlX::ArraySkip

XS Backend

If you install PerlX::ArraySkip::XS, a faster XS-based implementation will be used instead of the pure Perl function. My basic benchmarking experiments seem to show this to be around 55% faster.

Calling PerlX::ArraySkip::IMPLEMENTATION will return "PP" or "XS" to reveal the implementation currently in use.

Environment

The environment variable PERLX_ARRAYSKIP_IMPLEMENTATION may be set to "PP" to prevent the XS backend from loading.

BUGS ^

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=PerlX-ArraySkip.

SEE ALSO ^

If you liked this, you might also like PerlX::Maybe.

AUTHOR ^

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE ^

To the extent possible under law, Toby Inkster has waived all copyright and related or neighbouring rights to PerlX::ArraySkip. This work is published from the United Kingdom.

http://creativecommons.org/publicdomain/zero/1.0/.

DISCLAIMER OF WARRANTIES ^

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

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