Moose::Util::TypeConstUsertContributed Perl DocMoose::Util::TypeConstraints(3)NAMEMoose::Util::TypeConstraints - Type constraint system for Moose
VERSION
version 2.1005
SYNOPSIS
use Moose::Util::TypeConstraints;
subtype 'Natural',
as 'Int',
where { $_ > 0 };
subtype 'NaturalLessThanTen',
as 'Natural',
where { $_ < 10 },
message { "This number ($_) is not less than ten!" };
coerce 'Num',
from 'Str',
via { 0+$_ };
class_type 'DateTimeClass', { class => 'DateTime' };
role_type 'Barks', { role => 'Some::Library::Role::Barks' };
enum 'RGBColors', [qw(red green blue)];
union 'StringOrArray', [qw( String Array )];
no Moose::Util::TypeConstraints;
DESCRIPTION
This module provides Moose with the ability to create custom type
constraints to be used in attribute definition.
Important Caveat
This is NOT a type system for Perl 5. These are type constraints, and
they are not used by Moose unless you tell it to. No type inference is
performed, expressions are not typed, etc. etc. etc.
A type constraint is at heart a small "check if a value is valid"
function. A constraint can be associated with an attribute. This
simplifies parameter validation, and makes your code clearer to read,
because you can refer to constraints by name.
Slightly Less Important Caveat
It is always a good idea to quote your type names.
This prevents Perl from trying to execute the call as an indirect
object call. This can be an issue when you have a subtype with the same
name as a valid class.
For instance:
subtype DateTime => as Object => where { $_->isa('DateTime') };
will just work, while this:
use DateTime;
subtype DateTime => as Object => where { $_->isa('DateTime') };
will fail silently and cause many headaches. The simple way to solve
this, as well as future proof your subtypes from classes which have yet
to have been created, is to quote the type name:
use DateTime;
subtype 'DateTime', as 'Object', where { $_->isa('DateTime') };
Default Type Constraints
This module also provides a simple hierarchy for Perl 5 types, here is
that hierarchy represented visually.
Any
Item
Bool
Maybe[`a]
Undef
Defined
Value
Str
Num
Int
ClassName
RoleName
Ref
ScalarRef[`a]
ArrayRef[`a]
HashRef[`a]
CodeRef
RegexpRef
GlobRef
FileHandle
Object
NOTE: Any type followed by a type parameter "[`a]" can be
parameterized, this means you can say:
ArrayRef[Int] # an array of integers
HashRef[CodeRef] # a hash of str to CODE ref mappings
ScalarRef[Int] # a reference to an integer
Maybe[Str] # value may be a string, may be undefined
If Moose finds a name in brackets that it does not recognize as an
existing type, it assumes that this is a class name, for example
"ArrayRef[DateTime]".
NOTE: Unless you parameterize a type, then it is invalid to include the
square brackets. I.e. "ArrayRef[]" will be treated as a new type name,
not as a parameterization of "ArrayRef".
NOTE: The "Undef" type constraint for the most part works correctly
now, but edge cases may still exist, please use it sparingly.
NOTE: The "ClassName" type constraint does a complex package existence
check. This means that your class must be loaded for this type
constraint to pass.
NOTE: The "RoleName" constraint checks a string is a package name which
is a role, like 'MyApp::Role::Comparable'.
Type Constraint Naming
Type name declared via this module can only contain alphanumeric
characters, colons (:), and periods (.).
Since the types created by this module are global, it is suggested that
you namespace your types just as you would namespace your modules. So
instead of creating a Color type for your My::Graphics module, you
would call the type My::Graphics::Types::Color instead.
Use with Other Constraint Modules
This module can play nicely with other constraint modules with some
slight tweaking. The "where" clause in types is expected to be a "CODE"
reference which checks its first argument and returns a boolean. Since
most constraint modules work in a similar way, it should be simple to
adapt them to work with Moose.
For instance, this is how you could use it with
Declare::Constraints::Simple to declare a completely new type.
type 'HashOfArrayOfObjects',
where {
IsHashRef(
-keys => HasLength,
-values => IsArrayRef(IsObject)
)->(@_);
};
For more examples see the t/examples/example_w_DCS.t test file.
Here is an example of using Test::Deep and its non-test related
"eq_deeply" function.
type 'ArrayOfHashOfBarsAndRandomNumbers',
where {
eq_deeply($_,
array_each(subhashof({
bar => isa('Bar'),
random_number => ignore()
})))
};
For a complete example see the t/examples/example_w_TestDeep.t test
file.
Error messages
Type constraints can also specify custom error messages, for when they
fail to validate. This is provided as just another coderef, which
receives the invalid value in $_, as in:
subtype 'PositiveInt',
as 'Int',
where { $_ > 0 },
message { "$_ is not a positive integer!" };
If no message is specified, a default message will be used, which
indicates which type constraint was being used and what value failed.
If Devel::PartialDump (version 0.14 or higher) is installed, it will be
used to display the invalid value, otherwise it will just be printed as
is.
FUNCTIONS
Type Constraint Constructors
The following functions are used to create type constraints. They will
also register the type constraints your create in a global registry
that is used to look types up by name.
See the "SYNOPSIS" for an example of how to use these.
subtype 'Name', as 'Parent', where { } ...
This creates a named subtype.
If you provide a parent that Moose does not recognize, it will
automatically create a new class type constraint for this name.
When creating a named type, the "subtype" function should either be
called with the sugar helpers ("where", "message", etc), or with a
name and a hashref of parameters:
subtype( 'Foo', { where => ..., message => ... } );
The valid hashref keys are "as" (the parent), "where", "message",
and "optimize_as".
subtype as 'Parent', where { } ...
This creates an unnamed subtype and will return the type constraint
meta-object, which will be an instance of
Moose::Meta::TypeConstraint.
When creating an anonymous type, the "subtype" function should
either be called with the sugar helpers ("where", "message", etc),
or with just a hashref of parameters:
subtype( { where => ..., message => ... } );
class_type ($class, ?$options)
Creates a new subtype of "Object" with the name $class and the
metaclass Moose::Meta::TypeConstraint::Class.
# Create a type called 'Box' which tests for objects which ->isa('Box')
class_type 'Box';
By default, the name of the type and the name of the class are the
same, but you can specify both separately.
# Create a type called 'Box' which tests for objects which ->isa('ObjectLibrary::Box');
class_type 'Box', { class => 'ObjectLibrary::Box' };
role_type ($role, ?$options)
Creates a "Role" type constraint with the name $role and the
metaclass Moose::Meta::TypeConstraint::Role.
# Create a type called 'Walks' which tests for objects which ->does('Walks')
role_type 'Walks';
By default, the name of the type and the name of the role are the
same, but you can specify both separately.
# Create a type called 'Walks' which tests for objects which ->does('MooseX::Role::Walks');
role_type 'Walks', { role => 'MooseX::Role::Walks' };
maybe_type ($type)
Creates a type constraint for either "undef" or something of the
given type.
duck_type ($name, \@methods)
This will create a subtype of Object and test to make sure the
value "can()" do the methods in "\@methods".
This is intended as an easy way to accept non-Moose objects that
provide a certain interface. If you're using Moose classes, we
recommend that you use a "requires"-only Role instead.
duck_type (\@methods)
If passed an ARRAY reference as the only parameter instead of the
$name, "\@methods" pair, this will create an unnamed duck type.
This can be used in an attribute definition like so:
has 'cache' => (
is => 'ro',
isa => duck_type( [qw( get_set )] ),
);
enum ($name, \@values)
This will create a basic subtype for a given set of strings. The
resulting constraint will be a subtype of "Str" and will match any
of the items in "\@values". It is case sensitive. See the
"SYNOPSIS" for a simple example.
NOTE: This is not a true proper enum type, it is simply a
convenient constraint builder.
enum (\@values)
If passed an ARRAY reference as the only parameter instead of the
$name, "\@values" pair, this will create an unnamed enum. This can
then be used in an attribute definition like so:
has 'sort_order' => (
is => 'ro',
isa => enum([qw[ ascending descending ]]),
);
union ($name, \@constraints)
This will create a basic subtype where any of the provided
constraints may match in order to satisfy this constraint.
union (\@constraints)
If passed an ARRAY reference as the only parameter instead of the
$name, "\@constraints" pair, this will create an unnamed union.
This can then be used in an attribute definition like so:
has 'items' => (
is => 'ro',
isa => union([qw[ Str ArrayRef ]]),
);
This is similar to the existing string union:
isa => 'Str|ArrayRef'
except that it supports anonymous elements as child constraints:
has 'color' => (
isa => 'ro',
isa => union([ 'Int', enum([qw[ red green blue ]]) ]),
);
as 'Parent'
This is just sugar for the type constraint construction syntax.
It takes a single argument, which is the name of a parent type.
where { ... }
This is just sugar for the type constraint construction syntax.
It takes a subroutine reference as an argument. When the type
constraint is tested, the reference is run with the value to be
tested in $_. This reference should return true or false to
indicate whether or not the constraint check passed.
message { ... }
This is just sugar for the type constraint construction syntax.
It takes a subroutine reference as an argument. When the type
constraint fails, then the code block is run with the value
provided in $_. This reference should return a string, which will
be used in the text of the exception thrown.
inline_as { ... }
This can be used to define a "hand optimized" inlinable version of
your type constraint.
You provide a subroutine which will be called as a method on a
Moose::Meta::TypeConstraint object. It will receive a single
parameter, the name of the variable to check, typically something
like "$_" or "$_[0]".
The subroutine should return a code string suitable for inlining.
You can assume that the check will be wrapped in parentheses when
it is inlined.
The inlined code should include any checks that your type's parent
types do. If your parent type constraint defines its own inlining,
you can simply use that to avoid repeating code. For example, here
is the inlining code for the "Value" type, which is a subtype of
"Defined":
sub {
$_[0]->parent()->_inline_check($_[1])
. ' && !ref(' . $_[1] . ')'
}
optimize_as { ... }
This feature is deprecated, use "inline_as" instead.
This can be used to define a "hand optimized" version of your type
constraint which can be used to avoid traversing a subtype
constraint hierarchy.
NOTE: You should only use this if you know what you are doing. All
the built in types use this, so your subtypes (assuming they are
shallow) will not likely need to use this.
type 'Name', where { } ...
This creates a base type, which has no parent.
The "type" function should either be called with the sugar helpers
("where", "message", etc), or with a name and a hashref of
parameters:
type( 'Foo', { where => ..., message => ... } );
The valid hashref keys are "where", "message", and "inlined_as".
Type Constraint Utilities
match_on_type $value => ( $type => \&action, ... ?\&default )
This is a utility function for doing simple type based dispatching
similar to match/case in OCaml and case/of in Haskell. It is not as
featureful as those languages, nor does not it support any kind of
automatic destructuring bind. Here is a simple Perl pretty printer
dispatching over the core Moose types.
sub ppprint {
my $x = shift;
match_on_type $x => (
HashRef => sub {
my $hash = shift;
'{ '
. (
join ", " => map { $_ . ' => ' . ppprint( $hash->{$_} ) }
sort keys %$hash
) . ' }';
},
ArrayRef => sub {
my $array = shift;
'[ ' . ( join ", " => map { ppprint($_) } @$array ) . ' ]';
},
CodeRef => sub {'sub { ... }'},
RegexpRef => sub { 'qr/' . $_ . '/' },
GlobRef => sub { '*' . B::svref_2object($_)->NAME },
Object => sub { $_->can('to_string') ? $_->to_string : $_ },
ScalarRef => sub { '\\' . ppprint( ${$_} ) },
Num => sub {$_},
Str => sub { '"' . $_ . '"' },
Undef => sub {'undef'},
=> sub { die "I don't know what $_ is" }
);
}
Or a simple JSON serializer:
sub to_json {
my $x = shift;
match_on_type $x => (
HashRef => sub {
my $hash = shift;
'{ '
. (
join ", " =>
map { '"' . $_ . '" : ' . to_json( $hash->{$_} ) }
sort keys %$hash
) . ' }';
},
ArrayRef => sub {
my $array = shift;
'[ ' . ( join ", " => map { to_json($_) } @$array ) . ' ]';
},
Num => sub {$_},
Str => sub { '"' . $_ . '"' },
Undef => sub {'null'},
=> sub { die "$_ is not acceptable json type" }
);
}
The matcher is done by mapping a $type to an "\&action". The $type
can be either a string type or a Moose::Meta::TypeConstraint
object, and "\&action" is a subroutine reference. This function
will dispatch on the first match for $value. It is possible to have
a catch-all by providing an additional subroutine reference as the
final argument to "match_on_type".
Type Coercion Constructors
You can define coercions for type constraints, which allow you to
automatically transform values to something valid for the type
constraint. If you ask your accessor to coerce, then Moose will run the
type-coercion code first, followed by the type constraint check. This
feature should be used carefully as it is very powerful and could
easily take off a limb if you are not careful.
See the "SYNOPSIS" for an example of how to use these.
coerce 'Name', from 'OtherName', via { ... }
This defines a coercion from one type to another. The "Name"
argument is the type you are coercing to.
To define multiple coercions, supply more sets of from/via pairs:
coerce 'Name',
from 'OtherName', via { ... },
from 'ThirdName', via { ... };
from 'OtherName'
This is just sugar for the type coercion construction syntax.
It takes a single type name (or type object), which is the type
being coerced from.
via { ... }
This is just sugar for the type coercion construction syntax.
It takes a subroutine reference. This reference will be called with
the value to be coerced in $_. It is expected to return a new value
of the proper type for the coercion.
Creating and Finding Type Constraints
These are additional functions for creating and finding type
constraints. Most of these functions are not available for importing.
The ones that are importable as specified.
find_type_constraint($type_name)
This function can be used to locate the Moose::Meta::TypeConstraint
object for a named type.
This function is importable.
register_type_constraint($type_object)
This function will register a Moose::Meta::TypeConstraint with the
global type registry.
This function is importable.
normalize_type_constraint_name($type_constraint_name)
This method takes a type constraint name and returns the normalized
form. This removes any whitespace in the string.
create_type_constraint_union($pipe_separated_types |
@type_constraint_names)
create_named_type_constraint_union($name, $pipe_separated_types |
@type_constraint_names)
This can take a union type specification like 'Int|ArrayRef[Int]',
or a list of names. It returns a new
Moose::Meta::TypeConstraint::Union object.
create_parameterized_type_constraint($type_name)
Given a $type_name in the form of 'BaseType[ContainerType]', this
will create a new Moose::Meta::TypeConstraint::Parameterized
object. The "BaseType" must exist already exist as a
parameterizable type.
create_class_type_constraint($class, $options)
Given a class name this function will create a new
Moose::Meta::TypeConstraint::Class object for that class name.
The $options is a hash reference that will be passed to the
Moose::Meta::TypeConstraint::Class constructor (as a hash).
create_role_type_constraint($role, $options)
Given a role name this function will create a new
Moose::Meta::TypeConstraint::Role object for that role name.
The $options is a hash reference that will be passed to the
Moose::Meta::TypeConstraint::Role constructor (as a hash).
create_enum_type_constraint($name, $values)
Given a enum name this function will create a new
Moose::Meta::TypeConstraint::Enum object for that enum name.
create_duck_type_constraint($name, $methods)
Given a duck type name this function will create a new
Moose::Meta::TypeConstraint::DuckType object for that enum name.
find_or_parse_type_constraint($type_name)
Given a type name, this first attempts to find a matching
constraint in the global registry.
If the type name is a union or parameterized type, it will create a
new object of the appropriate, but if given a "regular" type that
does not yet exist, it simply returns false.
When given a union or parameterized type, the member or base type
must already exist.
If it creates a new union or parameterized type, it will add it to
the global registry.
find_or_create_isa_type_constraint($type_name)
find_or_create_does_type_constraint($type_name)
These functions will first call "find_or_parse_type_constraint". If
that function does not return a type, a new type object will be
created.
The "isa" variant will use "create_class_type_constraint" and the
"does" variant will use "create_role_type_constraint".
get_type_constraint_registry
Returns the Moose::Meta::TypeConstraint::Registry object which
keeps track of all type constraints.
list_all_type_constraints
This will return a list of type constraint names in the global
registry. You can then fetch the actual type object using
"find_type_constraint($type_name)".
list_all_builtin_type_constraints
This will return a list of builtin type constraints, meaning those
which are defined in this module. See the "Default Type
Constraints" section for a complete list.
export_type_constraints_as_functions
This will export all the current type constraints as functions into
the caller's namespace ("Int()", "Str()", etc). Right now, this is
mostly used for testing, but it might prove useful to others.
get_all_parameterizable_types
This returns all the parameterizable types that have been
registered, as a list of type objects.
add_parameterizable_type($type)
Adds $type to the list of parameterizable types
BUGS
See "BUGS" in Moose for details on reporting bugs.
AUTHOR
Moose is maintained by the Moose Cabal, along with the help of many
contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
details.
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Infinity Interactive, Inc..
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.18.1 2013-08-07 Moose::Util::TypeConstraints(3)
