Perl::Critic::Policy::RegularExpressions::ProhibitFixedStringMatches3pm

Affiliation

This Policy is part of the core Perl::Critic distribution.

Overview

A regular expression that matches just a fixed set of constant strings is wasteful of performance and is hard on maintainers. It is much more readable and often faster to use "eq" or a hash to match such strings.

    # Bad
    my $is_file_function = $token =~ m/\A (?: open | close | read ) \z/xms;
    # Faster and more readable
    my $is_file_function = $token eq 'open' ||
                           $token eq 'close' ||
                           $token eq 'read';

For larger numbers of strings, a hash is superior:

    # Bad
    my $is_perl_keyword =
        $token =~ m/\A (?: chomp | chop | chr | crypt | hex | index
                           lc | lcfirst | length | oct | ord | ... ) \z/xms;
    # Better
    Readonly::Hash my %PERL_KEYWORDS => map {$_ => 1} qw(
        chomp chop chr crypt hex index lc lcfirst length oct ord ...
    );
    my $is_perl_keyword = $PERL_KEYWORD{$token};

Conway also suggests using lc() instead of a case-insensitive match.

    m/^foo$/;
    m/\A foo \z/x;
    m/\A foo \z/xm;
    m/\A(foo)\z/;
    m/\A(?:foo)\z/;
    m/\A(foo|bar)\z/;
    m/\A(?:foo|bar)\z/;

Configuration

This Policy is not configurable except for the standard options.

Credits

Initial development of this policy was supported by a grant from the Perl Foundation.