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Kevin Ryde


Perl::Critic::Policy::ValuesAndExpressions::ProhibitBarewordDoubleColon - don't use Foo:: style barewords


This policy is part of the Perl::Critic::Pulp add-on. It asks you not to use the double-colon bareword like

    $class = Foo::Bar::;     # bad

but instead a plain string

    $class = 'Foo::Bar';     # ok

This is intended as a building block for a restricted coding style, or a matter of personal preference if you think the :: is a bit obscure and that it's clearer to write a string when you mean a string. On that basis the policy is lowest priority and under the "cosmetic" theme (see "POLICY THEMES" in Perl::Critic).

Indirect Object Syntax

By default a double-colon is allowed in the indirect object syntax (see "Indirect Object Syntax" in perlobj).

    my $obj = new Foo::Bar:: $arg1,$arg2;   # ok

This is because :: there is important to disambiguate a class name Foo::Bar from a function Foo::Bar(), ie. function Bar() in package Foo.

Whether you actually want indirect object syntax is a matter for other policies, like ProhibitIndirectSyntax. If you don't want the double-colon bareword then change to arrow style Foo::Bar->new($arg,...).

Double-Colon Advantages

The :: bareword is for use on package names, not general bareword quoting. If there's no such package at compile time a warning is given (see "Bareword "%s" refers to nonexistent package" in perldiag)

    my $class = No::Such::Package::;  # Perl warning

This warning can help pick up typos, though it relies on relevant packages being loaded at compile-time (ie. BEGIN). If the package is loaded by a require at runtime then the warning fires even though the code runs correctly. For reference, a warning isn't given for the indirect object syntax, which rather limits its benefit.


If you don't care about this you can always disable ProhibitBarewordDoubleColon from your .perlcriticrc in the usual way (see "CONFIGURATION" in Perl::Critic),



allow_indirect_syntax (boolean, default true)

If true then allow double-colon in the indirect object syntax as shown above. If false then report double-colons everywhere as violations

    # bad under allow_indirect_syntax=false
    my $obj = new Foo::Bar:: $arg1,$arg2;

This can be controlled from your ~/.perlcriticrc in the usual way. For example



Perl::Critic::Pulp, Perl::Critic, Perl::Critic::Policy::Objects::ProhibitIndirectSyntax

"Foo:: can be used as implicitly quoted package name" in perl5005delta




Copyright 2010, 2011, 2012, 2013, 2014, 2015 Kevin Ryde

Perl-Critic-Pulp is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

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