Choosing Between Moose, Moo, and Classic bless for New Perl Projects

Decision and Constraints

For a new Perl project you need an object system that balances feature richness with low overhead. The constraints are: minimal runtime dependencies, fast startup, compatibility with Perl 5.10+, and straightforward maintenance.

Options Comparison

Feature	Moose	Moo	Classic bless
Core dependencies	None (but requires XS)	None (pure Perl)	None
Attribute handling	Moose::Attribute	Moo::Attribute	Manual
Method modifiers	before/after/around	limited	None
Meta‑object protocol	Full MOP	Subset (Moo::Role)	None
Startup overhead	Higher (~30‑50 ms)	Lower (~5‑10 ms)	Negligible

Trade‑offs

Moose provides the most expressive introspection and composability, but its XS dependencies increase memory use and compile time. Moo offers a Moose‑like declarative syntax with far less overhead, making it suitable for most applications where advanced MOP features are not required. Classic bless gives ultimate control and zero dependencies, but lacks reusable attribute handling and method modifiers, leading to more boilerplate.

Implementation Example

The following example shows a simple Person class built with Moo, including attributes, a method, and a basic type check.

#!/usr/bin/env perl
use strict;
use warnings;
use Moo;
use Types::Standard qw(Str Int);

has name => (is => 'ro', isa => Str, required => 1);
has age  => (is => 'rw', isa => Int, default => sub { 0 });

sub greet {
    my $self = shift;
    return sprintf('Hello, I am %s and I am %d years old.',
                   $self->name, $self->age);
}

1;

To use the class:

#!/usr/bin/env perl
use strict;
use warnings;
use Person;

my $bob = Person->new(name => 'Bob', age => 42);
print $bob->greet, "\n";

Verification Steps

1. Install Moo (if not present): cpanm Moo
2. Check syntax: perl -c person.pl (should exit with no errors)
3. Run the script: perl person.pl; expected output resembles Hello, I am Bob and I am 42 years old.
4. Confirm Moo loads: perl -MMoo -e 'print q{Moo loaded}\''
5. Optional startup comparison: time perl -MMoo -e 1 vs. time perl -Moose -e 1; Moo typically shows lower real time.

Limitations and Practical Checks

• Moo does not natively support Moose attribute traits such as Lazy or AutoDeref; you need extra plugins like MooX::Lazy if those features are required.
• When mixing Moo classes with Moose roles, use Moo::Role or Moose::Exporter to avoid incompatibility.
• Startup measurements can vary with system load; run each timing command multiple times and take the median for a reliable comparison.