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Andy Lester > Perl-Critic-Bangs > Perl::Critic::Policy::Bangs::ProhibitRefProtoOrProto



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Perl::Critic::Policy::Bangs::ProhibitRefProtoOrProto - Create a clone() method if you need copies of objects.


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


Many times you'll see code for object constructors that's been cut-and-pasted from somewhere else, and it looks like this:

    sub new {
        my $proto = shift;
        my $class = ref($proto) || $proto;
        my $self  = bless {}, $class;

The $class is derived from the first parameter, whether it's the class name, or an existing object. This lets you do this:

    my $fido = Dog->new();

which is very common, and the less likely

    my $rover = $fido->new();

Now, why would you want to instantiate an object based on the type of another object? If you want to make $rover a clone of $fido, then Dog should have a clone() method, instead of overloading the meaning of new().

That's all the ref($proto) || $proto does for you. If you don't need that dubious functionality, then write your constructors like this:

    sub new {
        my $class = shift;
        my $self = bless {}, $class;

See also Randal Schwartz's take on it at


This Policy is not configurable except for the standard options.


Andrew Moore <>


Adapted from policies by Jeffrey Ryan Thalhammer <>, and work done by Andrew Moore <>.


Copyright (C) 2006-2013 Andy Lester

This library is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0.

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