Provided by: libclass-meta-perl_0.66-2_all 
NAME
Class::Meta::Type - Data type validation and accessor building.
SYNOPSIS
package MyApp::TypeDef;
use strict;
use Class::Meta::Type;
use IO::Socket;
my $type = Class::Meta::Type->add(
key => 'io_socket',
desc => 'IO::Socket object',
name => 'IO::Socket Object'
);
DESCRIPTION
This class stores the various data types us ed by "Class::Meta". It manages all aspects of
data type validation and method creation. New data types can be added to Class::Meta::Type
by means of the "add()" constructor. This is useful for creating custom types for your
Class::Meta-built classes.
Note:This class manages the most advanced features of "Class::Meta". Before deciding to
create your own accessor closures as described in add(), you should have a thorough
working knowledge of how Class::Meta works, and have studied the add() method carefully.
Simple data type definitions such as that shown in the SYNOPSIS, on the other hand, are
encouraged.
CONSTRUCTORS
new
my $type = Class::Meta::Type->new($key);
Returns the data type definition for an existing data type. The definition will be looked
up by the $key argument. Use "add()" to specify new types. If no data type exists for a
given key, but "Class::Meta->for_key" returns a Class::Meta::Class object for that key,
then "new()" will implicitly call "add()" to create add a new type corresponding to that
class. This makes it easy to use any Class::Meta class as a data type.
Other data types can be added by means of the "add()" constructor, or by simply "use"ing
one or more of the following modules:
Class::Meta::Types::Perl
scalar
scalarref
array
hash
code
Class::Meta::Types::String
string
Class::Meta::Types::Boolean
boolean
Class::Meta::Types::Numeric
whole
integer
decimal
real
float
Read the documentation for the individual modules for details on their data types.
add
my $type = Class::Meta::Type->add(
key => 'io_socket',
name => 'IO::Socket Object',
desc => 'IO::Socket object'
);
Creates a new data type definition and stores it for future use. Use this constructor to
add new data types to meet the needs of your class. The named parameter arguments are:
key Required. The key with which the data type can be looked up in the future via a call
to "new()". Note that the key will be used case-insensitively, so "foo", "Foo", and
"FOO" are equivalent, and the key must be unique.
name
Required. The name of the data type. This should be formatted for display purposes,
and indeed, Class::Meta will often use it in its own exceptions.
check
Optional. Specifies how to validate the value of an attribute of this type. The check
parameter can be specified in any of the following ways:
• As a code reference. When Class::Meta executes this code reference, it will pass
in the value to check, the object for which the attribute will be set, and the
Class::Meta::Attribute object describing the attribute. If the attribute is a
class attribute, then the second argument will not be an object, but a hash
reference with two keys:
$name The existing value for the attribute is stored under the attribute name.
__pkg The name of the package to which the attribute is being assigned.
If the new value is not the proper value for your custom data type, the code
reference should throw an exception. Here's an example; it's the code reference
used by "string" data type, which you can add to Class::Meta::Type simply by using
Class::Meta::Types::String:
check => sub {
my $value = shift;
return unless defined $value && ref $value;
require Carp;
our @CARP_NOT = qw(Class::Meta::Attribute);
Carp::croak("Value '$value' is not a valid string");
}
Here's another example. This code reference might be used to make sure that a new
value is always greater than the existing value.
check => sub {
my ($new_val, $obj, $attr) = @_;
# Just return if the new value is greater than the old value.
return if defined $new_val && $new_val > $_[1]->{$_[2]->get_name};
require Carp;
our @CARP_NOT = qw(Class::Meta::Attribute);
Carp::croak("Value '$new_val' is not greater than '$old_val'");
}
• As an array reference. All items in this array reference must be code references
that perform checks on a value, as specified above.
• As a string. In this case, Class::Meta::Type assumes that your data type
identifies a particular object type. Thus it will use the string to construct a
validation code reference for you. For example, if you wanted to create a data
type for IO::Socket objects, pass the string 'IO::Socket' to the check parameter
and Class::Meta::Type will use the code reference returned by
"class_validation_generator()" to generate the validation checks. If you'd like to
specify an alternative class validation code generator, pass one to the
"class_validation_generator()" class method. Or pass in a code reference or array
reference of code reference as just described to use your own validator once.
Note that if the "check" parameter is not specified, there will never be any
validation of your custom data type. And yes, there may be times when you want this --
The default "scalar" and "boolean" data types, for example, have no checks.
builder
Optional. This parameter specifies the accessor builder for attributes of this type.
The "builder" parameter can be any of the following values:
"default"
The string 'default' uses Class::Meta::Type's default accessor building code,
provided by Class::Meta::AccessorBuilder. This is the default value, of course.
"affordance"
The string 'default' uses Class::Meta::Type's affordance accessor building code,
provided by Class::Meta::AccessorBuilder::Affordance. Affordance accessors provide
two accessors for an attribute, a "get_*" accessor and a "set_*" mutator. See
Class::Meta::AccessorBuilder::Affordance for more information.
"semi-affordance"
The string 'default' uses Class::Meta::Type's semi-affordance accessor building
code, provided by Class::Meta::AccessorBuilder::SemiAffordance. Semi-affordance
accessors differ from affordance accessors in that they do not prepend "get_" to
the accessor. So for an attribute "foo", the accessor would be named "foo()" and
the mutator named "set_foo()". See Class::Meta::AccessorBuilder::SemiAffordance
for more information.
A Package Name
Pass in the name of a package that contains the functions "build()",
"build_attr_get()", and "build_attr_set()". These functions will be used to create
the necessary accessors for an attribute. See Custom Accessor Building for details
on creating your own accessor builders.
CLASS METHODS
default_builder
my $default_builder = Class::Meta::Type->default_builder;
Class::Meta::Type->default_builder($default_builder);
Get or set the default builder class attribute. The value can be any one of the values
specified for the "builder" parameter to add(). The value set in this attribute will be
used for the "builder" parameter to to add() when none is explicitly passed. Defaults to
"default".
class_validation_generator
my $gen = Class::Meta::Type->class_validation_generator;
Class::Meta::Type->class_validation_generator( sub {
my ($pkg, $name) = @_;
return sub {
die "'$pkg' is not a valid $name"
unless UNIVERSAL::isa($pkg, $name);
};
});
Gets or sets a code reference that will be used to generate the validation checks for
class data types. That is to say, it will be used when a string is passed to the "checks"
parameter to <add()> to generate the validation checking code for data types that are
objects. By default, it will generate a validation checker like this:
sub {
my $value = shift;
return if UNIVERSAL::isa($value, 'IO::Socket')
require Carp;
our @CARP_NOT = qw(Class::Meta::Attribute);
Carp::croak("Value '$value' is not a IO::Socket object");
};
But if you'd like to specify an alternate validation check generator--perhaps you'd like
to throw exception objects rather than use Carp--just pass a code reference to this class
method. The code reference should expect two arguments: the data type value to be
validated, and the string passed via the "checks" parameter to "add()". It should return a
code reference or array of code references that validate the value. For example, you might
want to do something like this to throw exception objects:
use Exception::Class('MyException');
Class::Meta::Type->class_validation_generator( sub {
my ($pkg, $type) = @_;
return [ sub {
my ($value, $object, $attr) = @_;
MyException->throw("Value '$value' is not a valid $type")
unless UNIVERSAL::isa($value, $pkg);
} ];
});
But if the default object data type validator is good enough for you, don't worry about
it.
INTERFACE
Instance Methods
key
my $key = $type->key;
Returns the key name for the type.
name
my $name = $type->name;
Returns the type name.
check
my $checks = $type->check;
my @checks = $type->check;
Returns an array reference or list of the data type validation code references for the
data type.
build
This is a protected method, designed to be called only by the Class::Meta::Attribute class
or a subclass of Class::Meta::Attribute. It creates accessors for the class that the
Class::Meta::Attribute object is a part of by calling out to the "build()" method of the
accessor builder class.
Although you should never call this method directly, subclasses of Class::Meta::Type may
need to override its behavior.
make_attr_set
This is a protected method, designed to be called only by the Class::Meta::Attribute class
or a subclass of Class::Meta::Attribute. It returns a reference to the attribute set
accessor (mutator) created by the call to "build()", and usable as an indirect attribute
accessor by the Class::Meta::Attribute "set()" method.
Although you should never call this method directly, subclasses of Class::Meta::Type may
need to override its behavior.
make_attr_get
This is a protected method, designed to be called only by the Class::Meta::Attribute class
or a subclass of Class::Meta::Attribute. It returns a reference to the attribute get
accessor created by the call to "build()", and usable as an indirect attribute accessor by
the Class::Meta::Attribute "get()" method.
Although you should never call this method directly, subclasses of Class::Meta::Type may
need to override its behavior.
CUSTOM DATA TYPES
Creating custom data types can be as simple as calling "add()" and passing in the name of
a class for the "check" parameter. This is especially useful when you just need to create
attributes that contain objects of a particular type, and you're happy with the accessors
that Class::Meta will create for you. For example, if you needed a data type for a
DateTime object, you can set it up--complete with validation of the data type, like this:
my $type = Class::Meta::Type->add(
key => 'datetime',
check => 'DateTime',
desc => 'DateTime object',
name => 'DateTime Object'
);
From then on, you can create attributes of the type "datetime" without any further work.
If you wanted to use affordance accessors, you'd simply add the requisite "builder"
attribute:
my $type = Class::Meta::Type->add(
key => 'datetime',
check => 'DateTime',
builder => 'affordance',
desc => 'DateTime object',
name => 'DateTime Object'
);
The same goes for using semi-affordance accessors.
Other than that, adding other data types is really a matter of the judicious use of the
"check" parameter. Ultimately, all attributes are scalar values. Whether they adhere to a
particular data type depends entirely on the validation code references passed via
"check". For example, if you wanted to create a "range" attribute with only the allowed
values 1-5, you could do it like this:
my $range_chk = sub {
my $value = shift;
die "Value is not a number" unless $value =~ /^[1..5]$/;
};
my $type = Class::Meta::Type->add(
key => 'range',
check => $range_chk,
desc => 'Pick a number between 1 and 5',
name => 'Range (1-5)'
);
Of course, the above value validator will throw an exception with the line number from
which "die" is called. Even better is to use Carp to throw an error with the file and line
number of the client code:
my $range_chk = sub {
my $value = shift;
return if $value =~ /^[1..5]$/;
require Carp;
our @CARP_NOT = qw(Class::Meta::Attribute);
Carp::croak("Value is not a number");
};
The "our @CARP_NOT" line prevents the context from being thrown from within
Class::Meta::Attribute, which is useful if you make use of that class' "set()" method.
Custom Accessor Building
Class::Meta also allows you to craft your own accessors. Perhaps you'd prefer to use a
StudlyCaps affordance accessor standard. In that case, you'll need to create your own
module that builds accessors. I recommend that you study Class::Meta::AccessorBuilder and
Class::Meta::AccessorBuilder::Affordance before taking on creating your own.
Custom accessor building modules must have three functions.
build
The "build()" function creates and installs the actual accessor methods in a class. It
should expect the following arguments:
sub build {
my ($class, $attribute, $create, @checks) = @_;
# ...
}
These are:
$class
The name of the class into which the accessors are to be installed.
$attribute
A Class::Meta::Attribute object representing the attribute for which accessors are to
be created. Use it to determine what types of accessors to create (read-only, write-
only, or read/write, class or object), and to add checks for required constraints and
accessibility (if the attribute is private, trusted, or protected).
$create
The value of the "create" parameter passed to Class::Meta::Attribute when the
attribute object was created. Use this argument to determine what type of accessor(s)
to create. See Class::Meta::Attribute for the possible values for this argument.
@checks
A list of one or more data type validation code references. Use these in any accessors
that set attribute values to check that the new value has a valid value.
See Class::Meta::AccessorBuilder for example attribute creation functions.
build_attr_get and build_attr_set
The "build_attr_get()" and "build_attr_set()" functions take a single argument, a
Class::Meta::Attribute object, and return code references that either represent the
corresponding methods, or that call the appropriate accessor methods to get and set an
attribute, respectively. The code references will be used by Class::Meta::Attribute's
"get()" and "set()" methods to get and set attribute values. Again, see
Class::Meta::AccessorBuilder for examples before creating your own.
SUPPORT
This module is stored in an open GitHub repository <http://github.com/theory/class-meta/>.
Feel free to fork and contribute!
Please file bug reports via GitHub Issues <http://github.com/theory/class-meta/issues/> or
by sending mail to bug-Class-Meta@rt.cpan.org <mailto:bug-Class-Meta@rt.cpan.org>.
AUTHOR
David E. Wheeler <david@justatheory.com>
SEE ALSO
Other classes of interest within the Class::Meta distribution include:
Class::Meta
This class contains most of the documentation you need to get started with
Class::Meta.
Class::Meta::Attribute
This class manages Class::Meta class attributes, all of which are based on data types.
These modules provide some data types to get you started:
Class::Meta::Types::Perl
Class::Meta::Types::String
Class::Meta::Types::Boolean
Class::Meta::Types::Numeric
The modules that Class::Meta comes with for creating accessors are:
Class::Meta::AccessorBuilder
Standard Perl-style accessors.
Class::Meta::AccessorBuilder::Affordance
Affordance accessors--that is, explicit and independent get and set accessors.
Class::Meta::AccessorBuilder::SemiAffordance
Semi-affordance accessors--that is, independent get and set accessors with an explicit
set accessor.
COPYRIGHT AND LICENSE
Copyright (c) 2002-2011, David E. Wheeler. Some Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.