Vincent Pit


Sub::Prototype::Util - Prototype-related utility routines.


Version 0.11


    use Sub::Prototype::Util qw<flatten wrap recall>;

    my @a = qw<a b c>;
    my @args = ( \@a, 1, { d => 2 }, undef, 3 );

    my @flat = flatten '\@$;$', @args;
    # @flat contains now ('a', 'b', 'c', 1, { d => 2 })

    my $res = recall 'CORE::push', @args;
    # @a contains now 'a', 'b', 'c', 1, { d => 2 }, undef, 3
    # and $res is 7

    my $splice = wrap 'CORE::splice';
    my @b = $splice->(\@a, 4, 2);
    # @a contains now ('a', 'b', 'c', 1, 3)
    # and @b is ({ d => 2 }, undef)


Prototypes are evil, but sometimes you just have to bear with them, especially when messing with core functions. This module provides several utilities aimed at facilitating "overloading" of prototyped functions.

They all handle 5.10's _ prototype.



    my @flattened = flatten($proto, @args);

Flattens the array @args according to the prototype $proto. When @args is what @_ is after calling a subroutine with prototype $proto, flatten returns the list of what @_ would have been if there were no prototype. It croaks if the arguments can't possibly match the required prototype, e.g. when a reference type is wrong or when not enough elements were provided.


    my $wrapper = wrap($name, %opts);
    my $wrapper = wrap({ $name => $proto }, %opts);

Generates a wrapper that calls the function $name with a prototyped argument list. That is, the wrapper's arguments should be what @_ is when you define a subroutine with the same prototype as $name.

    my $a = [ 0 .. 2 ];
    my $push = wrap 'CORE::push';
    $push->($a, 3, 4); # returns 3 + 2 = 5 and $a now contains 0 .. 4

You can force the use of a specific prototype. In this case, $name must be a hash reference that holds exactly one key / value pair, the key being the function name and the value the prototpye that should be used to call it.

    my $push = wrap { 'CORE::push' => '\@$' }; # only pushes 1 arg

The remaining arguments %opts are treated as key / value pairs that are meant to tune the code generated by "wrap". Valid keys are :

  • ref => $func

    Specifies the function used in the generated code to test the reference type of scalars. Defaults to 'ref'. You may also want to use "reftype" in Scalar::Util.

  • wrong_ref => $code

    The code executed when a reference of incorrect type is encountered. The result of this snippet is also the result of the generated code, hence it defaults to 'undef'. It's a good place to croak or die too.

  • sub => $bool

    Encloses the code into a sub { } block. Default is true.

  • compile => $bool

    Makes "wrap" compile the code generated and return the resulting code reference. Be careful that in this case ref must be a fully qualified function name. Defaults to true, but turned off when sub is false.

For example, this allows you to recall into CORE::grep and CORE::map by using the \&@ prototype :

    my $grep = wrap { 'CORE::grep' => '\&@' };
    # the prototypes are intentionally different
    sub mygrep (&@) { $grep->(@_) }


    my @res = recall($name, @args);
    my @res = recall({ $name => $proto }, @args);

Calls the function $name with the prototyped argument list @args. That is, @args should be what @_ is when you call a subroutine with $name as prototype. You can still force the prototype by passing { $name => $proto } as the first argument.

    my $a = [ ];
    recall { 'CORE::push' => '\@$' }, $a, 1, 2, 3; # $a just contains 1

It's implemented in terms of "wrap", and hence calls eval at each run. If you plan to recall several times, consider using "wrap" instead.


The functions "flatten", "wrap" and "recall" are only exported on request, either by providing their name or by the ':funcs' and ':all' tags.


Carp, Exporter (core modules since perl 5), Scalar::Util (since 5.7.3).


Vincent Pit, <perl at>,

You can contact me by mail or on (vincent).


Please report any bugs or feature requests to bug-sub-prototype-util at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Sub::Prototype::Util

Tests code coverage report is available at


Copyright 2008,2009,2010,2011,2013 Vincent Pit, all rights reserved.

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