# phpman > perldoc > MRO::Compat

## NAME
    [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) - mro::* interface compatibility for Perls < 5.9.5

## SYNOPSIS
       package PPP;      use base qw/Exporter/;
       package X;        use base qw/PPP/;
       package Y;        use base qw/PPP/;
       package Z;        use base qw/PPP/;

       package FooClass; use base qw/X Y Z/;

       package main;
       use [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown);
       my $linear = [mro::get_linear_isa](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Agetlinearisa/markdown)('FooClass');
       print join(q{, }, @$linear);

       # Prints: FooClass, X, PPP, Exporter, Y, Z

## DESCRIPTION
    The "mro" namespace provides several utilities for dealing with method resolution order and
    method caching in general in Perl 5.9.5 and higher.

    This module provides those interfaces for earlier versions of Perl (back to 5.6.0 anyways).

    It is a harmless no-op to use this module on 5.9.5+. That is to say, code which properly uses
    [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) will work unmodified on both older Perls and 5.9.5+.

    If you're writing a piece of software that would like to use the parts of 5.9.5+'s mro::
    interfaces that are supported here, and you want compatibility with older Perls, this is the
    module for you.

    Some parts of this code will work better and/or faster with [Class::C3::XS](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3%3A%3AXS/markdown) installed (which is an
    optional prereq of [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown), which is in turn a prereq of this package), but it's not a
    requirement.

    This module never exports any functions. All calls must be fully qualified with the "mro::"
    prefix.

    The interface documentation here serves only as a quick reference of what the function basically
    does, and what differences between [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) and 5.9.5+ one should look out for. The main docs
    in 5.9.5's mro are the real interface docs, and contain a lot of other useful information.

## Functions
  [mro::get_linear_isa](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Agetlinearisa/markdown)($classname[, $type])
    Returns an arrayref which is the linearized "ISA" of the given class. Uses whichever MRO is
    currently in effect for that class by default, or the given MRO (either "c3" or "dfs" if
    specified as $type).

    The linearized ISA of a class is a single ordered list of all of the classes that would be
    visited in the process of resolving a method on the given class, starting with itself. It does
    not include any duplicate entries.

    Note that "UNIVERSAL" (and any members of "UNIVERSAL"'s MRO) are not part of the MRO of a class,
    even though all classes implicitly inherit methods from "UNIVERSAL" and its parents.

  [mro::import](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Aimport/markdown)
    This allows the "use mro 'dfs'" and "use mro 'c3'" syntaxes, providing you "use [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown)"
    first. Please see the "USING C3" section for additional details.

  [mro::set_mro](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Asetmro/markdown)($classname, $type)
    Sets the mro of $classname to one of the types "dfs" or "c3". Please see the "USING C3" section
    for additional details.

  [mro::get_mro](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Agetmro/markdown)($classname)
    Returns the MRO of the given class (either "c3" or "dfs").

    It considers any [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown)-using class to have C3 MRO even before [Class::C3::initialize](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3%3A%3Ainitialize/markdown)() is
    called.

  [mro::get_isarev](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Agetisarev/markdown)($classname)
    Returns an arrayref of classes who are subclasses of the given classname. In other words,
    classes in whose @ISA hierarchy we appear, no matter how indirectly.

    This is much slower on pre-5.9.5 Perls with [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) than it is on 5.9.5+, as it has to
    search the entire package namespace.

  [mro::is_universal](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Aisuniversal/markdown)($classname)
    Returns a boolean status indicating whether or not the given classname is either "UNIVERSAL"
    itself, or one of "UNIVERSAL"'s parents by @ISA inheritance.

    Any class for which this function returns true is "universal" in the sense that all classes
    potentially inherit methods from it.

  [mro::invalidate_all_method_caches](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Ainvalidateallmethodcaches/markdown)
    Increments "PL_sub_generation", which invalidates method caching in all packages.

    Please note that this is rarely necessary, unless you are dealing with a situation which is
    known to confuse Perl's method caching.

  [mro::method_changed_in](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Amethodchangedin/markdown)($classname)
    Invalidates the method cache of any classes dependent on the given class. In [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) on
    pre-5.9.5 Perls, this is an alias for "[mro::invalidate_all_method_caches](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Ainvalidateallmethodcaches/markdown)" above, as pre-5.9.5
    Perls have no other way to do this. It will still enforce the requirement that you pass it a
    classname, for compatibility.

    Please note that this is rarely necessary, unless you are dealing with a situation which is
    known to confuse Perl's method caching.

  [mro::get_pkg_gen](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Agetpkggen/markdown)($classname)
    Returns an integer which is incremented every time a local method of or the @ISA of the given
    package changes on Perl 5.9.5+. On earlier Perls with this [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown) module, it will probably
    increment a lot more often than necessary.

## USING C3
    While this module makes the 5.9.5+ syntaxes "use mro 'c3'" and "[mro::set_mro](https://www.chedong.com/phpMan.php/perldoc/mro%3A%3Asetmro/markdown)("Foo", 'c3')"
    available on older Perls, it does so merely by passing off the work to [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown).

    It does not remove the need for you to call "[Class::C3::initialize](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3%3A%3Ainitialize/markdown)()",
    "[Class::C3::reinitialize](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3%3A%3Areinitialize/markdown)()", and/or "[Class::C3::uninitialize](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3%3A%3Auninitialize/markdown)()" at the appropriate times as
    documented in the [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown) docs. These three functions are always provided by [MRO::Compat](https://www.chedong.com/phpMan.php/perldoc/MRO%3A%3ACompat/markdown),
    either via [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown) itself on older Perls, or directly as no-ops on 5.9.5+.

## SEE ALSO
    [Class::C3](https://www.chedong.com/phpMan.php/perldoc/Class%3A%3AC3/markdown)

    mro

## AUTHOR
    Brandon L. Black, <<blblack@gmail.com>>

## COPYRIGHT AND LICENSE
    Copyright 2007-2008 Brandon L. Black <<blblack@gmail.com>>

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