# Moose Dependencies A Lurid Tale

Right so the rumor is that Moose has a lot of dependencies. I mean according to cpantesters Moose has 24 different dependencies! (Note: that same site says that almost all of those dependencies have a nearly 100% test record, but we’re talking Quantity not Quality!). Let’s examine this a bit more:

Here are the actual direct dependencies from Moose and Class::MOP’s Makefile.PLs

## Perl Core

First Perl … you must be at least version 5.8.1 to play, this means your perl has to have been released sometime after September 2003

Carp ships with 5.00 and above, so you’ve already got it

Scalar::Util 1.19 ships with 5.8.9. Moose has a dependency on 1.19+ because of known issues in earlier versions. We re-export blessed as well as use looks_like_number, refaddr, weaken, and set_prototype internally.

## Moose Only

We use zip, first_index, any, all, and uniq, these could be re-implemented but they’re in List::MoreUtils for a reason. Additionally the versions here are written in C so there’s very little performance hit.

“Sub::Exporter - a sophisticated exporter for custom-built routines”. Most of Moose’s advanced exporting features are based upon Sub::Exporter.

Sub::Exporter depends on Params::Util, Sub::Install, and Data::OptList.

“Data::OptList - parse and validate simple name/value option pairs”. We use mkopt internally in Moose::Util. Since Data::OptList is a dependency of a dependency already (Sub::Exporter) we can use it “for free”.

## Class::MOP Only

“MRO::Compat - mro interface compatibility for Perls < 5.9.5”. Perl 5.10.0 introduced a new mro pragma that made dealing with the inheritance tree much easier. This module provides backwards compatibility for that pragma.

Depends on Class::C3 which in turn depends on Algorithm::C3 but neither of which are used in Moose directly. Note that these two are baked into 5.10 and thus this entire set of dependencies is a null op under Perls released since 2007.

## Non-Core – Common between Moose & Class::MOP

“Devel::GlobalDestruction - Expose PL_dirty, the flag which marks global destruction.” We expose this as Class::MOP::in_global_destruction, though that is undocumented.

Depends on Scope::Guard and Sub::Exporter.

“Scope::Guard - lexically scoped resource management”. This creates a guard object, which is effectively an object that triggers a cleanup function when it is garbage collected.

“Sub::Name - (re)name a sub”. We expose this as Class::MOP::subname, which is used extensively internally in both Class::MOP and Moose.

“Task::Weaken - Ensure that a platform has weaken support”. Scalar::Util sometimes comes in a pure perl variant that lacks the weaken function that Moose uses. This ensures that feature is present even on broken installations.

## Removed Dependencies

• Sub::Identify

This has been folded into Class::MOP directly. It was used to maintain Pure Perl compatibility but that effort was abandoned when maintenance became a nightmare and we discovered we were never gonna have 100% compatibility between Pure Perl and XS.

• Test::Output: 0.09

This has become optional.

## Required for Tests

Moose and Class::MOP have over 5519 core tests. We depend heavily on Test::More and Test::Exception and several optional modules that if you have them installed will run extra tests.

“Test::More - yet another framework for writing test scripts.” Test::More 0.80 ships with Perl 5.8.9.

“Test::Exception - Test exception based code”. Provides lives_ok, throws_ok, dies_ok and lives_and that are used extensively in the Class::MOP and Moose test suites.

“File::Spec - portably perform operations on file names.” This shipped with 5.004. You have it installed.