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Acme-CPANModules-SmartMatch-0.007
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NAME

Acme::CPANModules::SmartMatch - List of modules to do smart matching

VERSION

This document describes version 0.007 of Acme::CPANModules::SmartMatch (from Perl distribution Acme-CPANModules-SmartMatch), released on 2024-07-01.

DESCRIPTION

About smart match

Smart matching, via the operator ~~, was introduced in perl 5.10 (released 2007). It's inspired by Perl 6 (now called Raku)'s given/when and/or Ruby's case and === operator that can "do the right/smart thing" in a case statement. Smart matching was indeed introduced along the new switch in perl 5.10.

What can smart match do? A whole lot. It can do string equality like eq if given a string on the left hand side and a string on the right hand side. Or it can do numeric equality like == when both sides are numbers. It can do regex matching like =~ if the left hand side is a scalar and the right hand side is a regexp.

But wait, there's (much) more. Interesting things begin when the left/right hand side is an array/hash/code/object. $str ~~ @ary_of_strs, probably the most common use-case for smart matching, can do value-in-array checking, equivalent to grep { $str eq $_ } @ary_of_strs but with short-circuiting capability. Then there's $re ~~ @ary_of_strs which can perform regex matching over the elements of array. Now what about when the right hand side is an arrayref or hashref? Or the left hand side? What if the array is an array of regexes instead? Or a mix of other types?

You need a full-page table as a reference of what will happen in smart matching, depending on the combination of operands. Things got complex real fast. Behaviors were changed from release to release, starting from 5.10.1. Then nobody was sure what smart matching should or should not do exactly.

In the end almost everyone agrees that smart matching is a bad fit for a weakly typed language like Perl. The programmer needs to be explicit on what type of operation should be done by specifying the appropriate /operator/ (e.g. == vs eq) instead of the operator deducing what operation needs to be done depending on the operand, because in Perl the operand's type is unclear. Mainly, a scalar can be a string, or a number, or a bool, or all.

The roadmap to removal

In perl 5.18 (2013), 6 years after being introduced and used by programmers without warning, smart match was declared as experimental, which is weird if you think about it. You now have to add use experimental "smartmatch" to silence the warning. What happens to the switch statement then? Since it's tied to smart matching, it also gets the same fate: became experimental in 5.18.

In perl 5.38 (2023) smart match is deprecated. You can no longer silence the warning with "use experimental 'smartmatch'" and must replace the use of smart match with something else.

Perl 5.42 (planned 2025) will finally remove smart match, resulting in a syntax error if you still use it.

Modules

However, if you still miss smart matching, some modules have been written to give you the same/similar feature.

match::smart (by TOBYINK, first released 2013, pure-perl) gives you a similar behaviour to perl's own ~~. It can be used as the |M| operator or as the match() function.

Switch::Back (by DCONWAY, first released in June 2024, pure-perl). Written by one of the designers of Perl 6, Switch::Back offers roughly the same feature set as the old switch and smartmatching. Although there's no longer ~~, just the smartmatch() function. So basically what match::smart offers, but 11 years later.

match::simple (by TOBYINK which is also the author of match::smart, first released in 2013, in the same distribution as match::smart, available in XS as well as pure-perl) offers a simplified version of smart matching. It has 8 kinds of behaviors depending only on the /right/ hand side.

Also see match::simple::sugar which gives you when, then, and numeric for use in a for() statement as a switch/use alternative.

Switch::Right (by DCONWAY, first released in June 2024, pure-perl). Also like TOBYINK with his duo of match::smart and match::simple, DCONWAY offers a companion to Switch::Back, a simplified/reimagined version of switch and smartmatching by simplifying the rules from 23 to just 6. The rules still depend on a mix of left and right operands.

Personal take

I personally haven't used switch all that much in Perl, though I used to use quite a bit of smartmatching in the 2010s, mostly the $str ~~ @ary_of_strs variant. I won't use match::smart or Switch::Back in any practical code any time soon (or ever), but which between match::simple and Switch::Right are the best compromise? I guess we'll have to see. In the mean time, see my benchmark in Bencher::ScenarioBundle::SmartMatch.

Other modules

Smart::Match (by LEONT, first released in 2011, pure-perl) offers a bunch of functions related to matching. Probably too low-level to use if you just want a smart match replacement.

ACME::CPANMODULES ENTRIES

match::smart

Author: TOBYINK

Switch::Back
match::simple

Author: TOBYINK

match::simple::sugar

Author: TOBYINK

Switch::Right
Bencher::ScenarioBundle::SmartMatch
Smart::Match

Author: LEONT

FAQ

What is an Acme::CPANModules::* module?

An Acme::CPANModules::* module, like this module, contains just a list of module names that share a common characteristics. It is a way to categorize modules and document CPAN. See Acme::CPANModules for more details.

What are ways to use this Acme::CPANModules module?

Aside from reading this Acme::CPANModules module's POD documentation, you can install all the listed modules (entries) using cpanm-cpanmodules script (from App::cpanm::cpanmodules distribution):

% cpanm-cpanmodules -n SmartMatch

Alternatively you can use the cpanmodules CLI (from App::cpanmodules distribution):

% cpanmodules ls-entries SmartMatch | cpanm -n

or Acme::CM::Get:

% perl -MAcme::CM::Get=SmartMatch -E'say $_->{module} for @{ $LIST->{entries} }' | cpanm -n

or directly:

% perl -MAcme::CPANModules::SmartMatch -E'say $_->{module} for @{ $Acme::CPANModules::SmartMatch::LIST->{entries} }' | cpanm -n

This Acme::CPANModules module also helps lcpan produce a more meaningful result for lcpan related-mods command when it comes to finding related modules for the modules listed in this Acme::CPANModules module. See App::lcpan::Cmd::related_mods for more details on how "related modules" are found.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Acme-CPANModules-SmartMatch.

SOURCE

Source repository is at https://github.com/perlancar/perl-Acme-CPANModules-SmartMatch.

SEE ALSO

Bencher::ScenarioBundle::SmartMatch

Acme::CPANModules - about the Acme::CPANModules namespace

cpanmodules - CLI tool to let you browse/view the lists

AUTHOR

perlancar <perlancar@cpan.org>

CONTRIBUTING

To contribute, you can send patches by email/via RT, or send pull requests on GitHub.

Most of the time, you don't need to build the distribution yourself. You can simply modify the code, then test via:

% prove -l

If you want to build the distribution (e.g. to try to install it locally on your system), you can install Dist::Zilla, Dist::Zilla::PluginBundle::Author::PERLANCAR, Pod::Weaver::PluginBundle::Author::PERLANCAR, and sometimes one or two other Dist::Zilla- and/or Pod::Weaver plugins. Any additional steps required beyond that are considered a bug and can be reported to me.

COPYRIGHT AND LICENSE

This software is copyright (c) 2024, 2023 by perlancar <perlancar@cpan.org>.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Acme-CPANModules-SmartMatch

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.