exact - Perl pseudo pragma to enable strict, warnings, features, mro, filehandle methods


version 1.13


Instead of this:

    use strict;
    use warnings;
    use utf8;
    use open ':std', ':utf8';
    use feature ':5.23';
    use feature qw( signatures refaliasing bitwise );
    use mro 'c3';
    use IO::File;
    use IO::Handle;
    use namespace::autoclean;
    use Carp qw( croak carp confess cluck );
    use Try::Tiny;

    no warnings "experimental::signatures";
    no warnings "experimental::refaliasing";
    no warnings "experimental::bitwise";

Type this:

    use exact;

Or for finer control, add some trailing modifiers like a line of the following:

    use exact -noexperiments, -fc, -signatures;
    use exact 5.16, -nostrict, -nowarnings, -noc3, -noutf8, -noautoclean;
    use exact '5.20';


exact is a Perl pseudo pragma to enable strict, warnings, features, mro, and filehandle methods along with a lot of other things, plus allow for easy extension via exact::* classes. The goal is to reduce header boilerplate, assuming defaults that seem to make sense but allowing overrides easily.

By default, exact will:

  • enable strictures (version 2)

  • load the latest feature bundle supported by the current Perl version

  • load all experimental features and switch off experimental warnings

  • set C3 style of mro

  • use utf8 in the source code context and set STDIN, STROUT, and STRERR to handle UTF8

  • enable methods on filehandles

  • import Carp's 4 methods

  • import Try::Tiny (kinda)


exact supports the following import flags:


This skips turning on the strict pragma.


This skips turning on the warnings pragma.


This skips turning on UTF8 in the source code context. Also skips setting STDIN, STDOUT, and STDERR to expect UTF8.


This skips setting C3 mro.


Normally, exact will look at your current version and find the highest supported feature bundle and enable it. Applying nobundle causes this behavior to be skipped. You can still explicitly set bundles yourself.


This skips enabling all features currently labled experimental by feature.


Normally, exact will disable experimental warnings. This skips that disabling step.


This skips using namespace::autoclean.


This skips importing the 4 Carp methods: croak, carp, confess, cluck.


This skips importing the functionality of Try::Tiny.


You can always provide a list of explicit features and bundles from feature. If provided, these will be enabled regardless of the other import flags set.

    use exact -noexperiments, -fc, -signatures;

Bundles provided can be exactly like those described in feature or in a variety of obvious forms:

  • :5.26

  • 5.26

  • v5.26

  • 26


It's possible to write extensions or plugins for exact to provide context-specific behavior, provided you are using Perl version 5.14 or newer. To activate these extensions, you need to provide their named suffix as a parameter to the use of exact.

    # will load "exact" and "exact::class";
    use exact -class;

    # will load "exact" and "exact::role" and turn off UTF8 features;
    use exact -role, -noutf8;

It's possible to provide parameters to the import method of the extension.

    # will load "exact" and "exact::answer" and pass "42" to the import method
    use exact 'answer(42)';

Writing Extensions

An extension may but is not required to have an import method. If such a method does exist, it will be passed: the package name, the name of the caller of exact, and any parameters passed.

    package exact::example;
    use exact;

    sub import {
        my ( $self, $caller, $params ) = @_;
        exact->monkey_patch( $caller, 'example' => \&example );

    sub example {
        say 42;



You can use exact to setup inheritance as follows:

    use exact 'SomeModule', 'SomeOtherModule';

This is roughly equivalent to:

    use exact;
    use parent 'SomeModule', 'SomeOtherModule';

See also the no_parent method.



Monkey patch functions into a given package.

    exact->monkey_patch( 'PackageName', add => sub { return $_[0] + $_[1] } );
        one   => sub { return 1 },
        two   => sub { return 2 },
        three => sub { return 3 },


This method will add a given parent to the @ISA of a given child.

    exact->add_isa( 'SuperClassParent', 'SubClassChild' );


Normally, if you specify a parent, it'll be added as a parent by inclusion in @INC. If you don't want to skip @INC inclusion, you can call no_parent in the import of the module being specified as a parent.

    sub import {


There may be a situation where you need an included parent to be listed last in @INC (at least relative to other parents). Normally, you'd do this by putting the name last in the list of modules. However, if for some reason you can't do that, you can call late_parent from the import of the parent that should be delayed in @INC inclusion.

    sub import {


You can look for additional information at:


Gryphon Shafer <>


This software is copyright (c) 2020 by Gryphon Shafer.

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