NAME
Class::Minion - Spartans! What is your API?
SYNOPSIS
package Example::Synopsis::Counter;
use Class::Minion
interface => [ qw( next ) ],
implementation => 'Example::Synopsis::Acme::Counter';
1;
# In a script near by ...
use Test::Most tests => 5;
use Example::Synopsis::Counter;
my $counter = Example::Synopsis::Counter->new;
is $counter->next => 0;
is $counter->next => 1;
is $counter->next => 2;
throws_ok { $counter->new } qr/Can't locate object method "new"/;
throws_ok { Example::Synopsis::Counter->next }
qr/Can't locate object method "next" via package "Example::Synopsis::Counter"/;
# And the implementation for this class:
package Example::Synopsis::Acme::Counter;
use strict;
our %__Meta = (
has => {
count => { default => 0 },
},
);
sub next {
my ($self) = @_;
$self->{$$}{count}++;
}
1; DESCRIPTION
Class::Minion is a class builder that simplifies the creation of loosely coupled Object Oriented systems.
Classes are built from a specification that declares the interface of the class (i.e. what commands minions of the classs respond to), as well as a package that provide the implementation of these commands.
The Object Oriented way as it was originally envisioned was more concerned with messaging, where in the words of Alan Kay (who coined the term "Object Oriented Programming") objects are "like biological cells and/or individual computers on a network, only able to communicate with messages" and "OOP to me means only messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things." (see The Deep Insights of Alan Kay for further inspiration).
This way of building is more likely to result in systems that are loosely coupled, modular and easy to maintain.
USAGE
Via Import
A class can be defined when importing Class::Minion e.g.
package Foo;
use Class::Minion
interface => [ qw( list of methods ) ],
construct_with => {
arg_name => {
assert => {
desc => sub {
# return true if arg is valid
# or false otherwise
}
},
optional => $boolean,
},
# ... other args
},
implementation => 'An::Implementation::Package',
;
1;Class::Minion->minionize([HASHREF])
A class can also be defined by calling the minionize() class method, with an optional hashref that specifies the class.
If the hashref is not given, the specification is read from a package variable named %__Meta in the package from which minionize() was called.
The class defined in the SYNOPSIS could also be defined like this
use Test::Most tests => 4;
use Class::Minion ();
my %Class = (
name => 'Counter',
interface => [qw( next )],
implementation => {
methods => {
next => sub {
my ($self) = @_;
$self->{$$}{count}++;
}
},
has => {
count => { default => 0 },
},
},
);
Class::Minion->minionize(\%Class);
my $counter = Counter->new;
is $counter->next => 0;
is $counter->next => 1;
throws_ok { $counter->new } qr/Can't locate object method "new"/;
throws_ok { Counter->next } qr/Can't locate object method "next" via package "Counter"/;Specification
The meaning of the keys in the specification hash are described next.
interface => ARRAYREF
A reference to an array containing the messages that minions belonging to this class should respond to. An exception is raised if this is empty or missing.
The messages named in this array must have corresponding subroutine definitions in a declared implementation, otherwise an exception is raised.
construct_with => HASHREF
An optional reference to a hash whose keys are the names of keyword parameters that are passed to the default constructor.
The values these keys are mapped to are themselves hash refs which can have the following keys.
optional => BOOLEAN (Default: false)
If this is set to a true value, then the corresponding key/value pair need not be passed to the constructor.
assert => HASHREF
A hash that maps a description to a unary predicate (i.e. a sub ref that takes one value and returns true or false). The default constructor will call these predicates to validate the parameters passed to it.
implementation => STRING | HASHREF
The name of a package that defines the subroutines declared in the interface.
The package may also contain other subroutines not declared in the interface that are for internal use in the package. These won't be callable using the $minion->command(...) syntax.
Alternatively an implementation can be hashref as shown in the synopsis above.
Configuring an implementation package
An implementation package can also be configured with a package variable %__Meta with the following keys:
has => HASHREF
This declares attributes of the implementation, mapping the name of an attribute to a hash with keys described in the following sub sections.
An attribute called "foo" can be accessed via it's object like this:
$self->{$$}{foo}i.e. the attribute name preceeded by two underscores. Objects created by Class::Minion are hashes, and are locked down to allow only keys declared in the "has" (implementation or role level) declarations. This is done to prevent accidents like mis-spelling an attribute name.
default => SCALAR | CODEREF
The default value assigned to the attribute when the object is created. This can be an anonymous sub, which will be excecuted to build the the default value (this would be needed if the default value is a reference, to prevent all objects from sharing the same reference).
assert => HASHREF
This is like the assert declared in a class package, except that these assertions are not run at construction time. Rather they are invoked by calling the semiprivate ASSERT routine.
handles => ARRAYREF | HASHREF | SCALAR
This declares that methods can be forwarded from the object to this attribute in one of three ways described below. These forwarding methods are generated as public methods if they are declared in the interface, and as semiprivate routines otherwise.
handles => ARRAYREF
All methods in the given array will be forwarded.
handles => HASHREF
Method forwarding will be set up such that a method whose name is a key in the given hash will be forwarded to a method whose name is the corresponding value in the hash.
handles => SCALAR
The scalar is assumed to be a role, and methods provided directly (i.e. not including methods in sub-roles) by the role will be forwarded.
reader => SCALAR
This can be a string which if present will be the name of a generated reader method.
This can also be the numerical value 1 in which case the generated reader method will have the same name as the key.
Readers should only be created if they are logically part of the class API.
semiprivate => ARRAYREF
Any subroutines in this list will be semiprivate, i.e. they will not be callable as regular object methods but can be called using the syntax:
$obj->{'!'}->do_something(...)roles => ARRAYREF
A reference to an array containing the names of one or more Role packages that define the subroutines declared in the interface.
The packages may also contain other subroutines not declared in the interface that are for internal use in the package. These won't be callable using the $minion->command(...) syntax.
Configuring a role package
A role package must be configured with a package variable %__Meta with the following keys (of which only "role" is mandatory):
role => 1 (Mandatory)
This indicates that the package is a Role.
has => HASHREF
This works the same way as in an implementation package.
semiprivate => ARRAYREF
This works the same way as in an implementation package.
requires => HASHREF
A hash with keys:
methods => ARRAYREF
Any methods listed here must be provided by an implementation package or a role.
attributes => ARRAYREF
Any attributes listed here must be provided by an implementation package or a role, or by the "requires" definition in the class.
Special Class Methods
These special class methods are useful in cases where the default constructor is not flexible enough and you need to write your own constructor.
__new__
This creates a new instance, in which attributes with declared defaults are populated with those defaults, and all others are populated with undef.
__build__
This can be used in a class method to invoke the semiprivate BUILD routine for an object after the object is created.
__assert__
Given the name of a declared attribute and a value, this routine validates the value using any assertions declared with the attribute.
Constructor Hooks
These are optional routines that can be used to customise the default construction process.
BUILDARGS
If this class method is defined, it will receive all parameters intended for new(), and its result (which should be a hash list or hashref) will be passed to new().
This is useful when the constructor requires positional rather than keyword parameters.
BUILD
If this semiprivate method is defined, it will be called by the default constructor and will receive the object and a hashref of named parameters that were passed to the constructor.
This is useful for carrying out any post-construction logic e.g. object validation.
BUGS
Please report any bugs or feature requests via the GitHub web interface at https://github.com/arunbear/perl5-minion/issues.
AUTHOR
Arun Prasaad <arunbear@cpan.org>
COPYRIGHT
Copyright 2014- Arun Prasaad
LICENSE
This library is free software; you can redistribute it and/or modify it under the terms of the GNU public license, version 3.