MooseX::Types::StructuUser3Contributed Perl DocumeMooseX::Types::Structured(3)NAMEMooseX::Types::Structured - MooseX::Types::Structured - Structured Type
Constraints for Moose
SYNOPSIS
The following is example usage for this module.
package Person;
use Moose;
use MooseX::Types::Moose qw(Str Int HashRef);
use MooseX::Types::Structured qw(Dict Tuple Optional);
## A name has a first and last part, but middle names are not required
has name => (
isa=>Dict[
first => Str,
last => Str,
middle => Optional[Str],
],
);
## description is a string field followed by a HashRef of tagged data.
has description => (
isa=>Tuple[
Str,
Optional[HashRef],
],
);
## Remainder of your class attributes and methods
Then you can instantiate this class with something like:
my $john = Person->new(
name => {
first => 'John',
middle => 'James'
last => 'Napiorkowski',
},
description => [
'A cool guy who loves Perl and Moose.', {
married_to => 'Vanessa Li',
born_in => 'USA',
};
]
);
Or with:
my $vanessa = Person->new(
name => {
first => 'Vanessa',
last => 'Li'
},
description => ['A great student!'],
);
But all of these would cause a constraint error for the 'name'
attribute:
## Value for 'name' not a HashRef
Person->new( name => 'John' );
## Value for 'name' has incorrect hash key and missing required keys
Person->new( name => {
first_name => 'John'
});
## Also incorrect keys
Person->new( name => {
first_name => 'John',
age => 39,
});
## key 'middle' incorrect type, should be a Str not a ArrayRef
Person->new( name => {
first => 'Vanessa',
middle => [1,2],
last => 'Li',
});
And these would cause a constraint error for the 'description'
attribute:
## Should be an ArrayRef
Person->new( description => 'Hello I am a String' );
## First element must be a string not a HashRef.
Person->new (description => [{
tag1 => 'value1',
tag2 => 'value2'
}]);
Please see the test cases for more examples.
DESCRIPTION
A structured type constraint is a standard container Moose type
constraint, such as an ArrayRef or HashRef, which has been enhanced to
allow you to explicitly name all the allowed type constraints inside
the structure. The generalized form is:
TypeConstraint[@TypeParameters or %TypeParameters]
Where 'TypeParameters' is an array reference or hash references of
Moose::Meta::TypeConstraint objects.
This type library enables structured type constraints. It is built on
top of the MooseX::Types library system, so you should review the
documentation for that if you are not familiar with it.
Comparing Parameterized types to Structured types
Parameterized constraints are built into core Moose and you are
probably already familiar with the type constraints 'HashRef' and
'ArrayRef'. Structured types have similar functionality, so their
syntax is likewise similar. For example, you could define a
parameterized constraint like:
subtype ArrayOfInts,
as ArrayRef[Int];
which would constrain a value to something like [1,2,3,...] and so on.
On the other hand, a structured type constraint explicitly names all
it's allowed 'internal' type parameter constraints. For the example:
subtype StringFollowedByInt,
as Tuple[Str,Int];
would constrain it's value to things like ['hello', 111] but ['hello',
'world'] would fail, as well as ['hello', 111, 'world'] and so on.
Here's another example:
package MyApp::Types;
use MooseX::Types -declare [qw(StringIntOptionalHashRef)];
use MooseX::Types::Moose qw(Str Int);
use MooseX::Types::Structured qw(Tuple Optional);
subtype StringIntOptionalHashRef,
as Tuple[
Str, Int,
Optional[HashRef]
];
This defines a type constraint that validates values like:
['Hello', 100, {key1 => 'value1', key2 => 'value2'}];
['World', 200];
Notice that the last type constraint in the structure is optional.
This is enabled via the helper Optional type constraint, which is a
variation of the core Moose type constraint 'Maybe'. The main
difference is that Optional type constraints are required to validate
if they exist, while 'Maybe' permits undefined values. So the
following example would not validate:
StringIntOptionalHashRef->validate(['Hello Undefined', 1000, undef]);
Please note the subtle difference between undefined and null. If you
wish to allow both null and undefined, you should use the core Moose
'Maybe' type constraint instead:
package MyApp::Types;
use MooseX::Types -declare [qw(StringIntMaybeHashRef)];
use MooseX::Types::Moose qw(Str Int Maybe);
use MooseX::Types::Structuredqw(Tuple);
subtype StringIntMaybeHashRef,
as Tuple[
Str, Int, Maybe[HashRef]
];
This would validate the following:
['Hello', 100, {key1 => 'value1', key2 => 'value2'}];
['World', 200, undef];
['World', 200];
Structured constraints are not limited to arrays. You can define a
structure against a HashRef with the 'Dict' type constaint as in this
example:
subtype FirstNameLastName,
as Dict[
firstname => Str,
lastname => Str,
];
This would constrain a HashRef that validates something like:
{firstname => 'Christopher', lastname => 'Parsons'};
but all the following would fail validation:
## Incorrect keys
{first => 'Christopher', last => 'Parsons'};
## Too many keys
{firstname => 'Christopher', lastname => 'Parsons', middlename => 'Allen'};
## Not a HashRef
['Christopher', 'Parsons'];
These structures can be as simple or elaborate as you wish. You can
even combine various structured, parameterized and simple constraints
all together:
subtype Crazy,
as Tuple[
Int,
Dict[name=>Str, age=>Int],
ArrayRef[Int]
];
Which would match:
[1, {name=>'John', age=>25},[10,11,12]];
Please notice how the type parameters can be visually arranged to your
liking and to improve the clarity of your meaning. You don't need to
run then altogether onto a single line. Additionally, since the 'Dict'
type constraint defines a hash constraint, the key order is not
meaningful. For example:
subtype AnyKeyOrder,
as Dict[
key1=>Int,
key2=>Str,
key3=>Int,
];
Would validate both:
{key1 => 1, key2 => "Hi!", key3 => 2};
{key2 => "Hi!", key1 => 100, key3 => 300};
As you would expect, since underneath its just a plain old Perl hash at
work.
Alternatives
You should exercise some care as to whether or not your complex
structured constraints would be better off contained by a real object
as in the following example:
package MyApp::MyStruct;
use Moose;
## lazy way to make a bunch of attributes
has $_ for qw(full_name age_in_years);
package MyApp::MyClass;
use Moose;
has person => (isa => 'MyApp::MyStruct');
my $instance = MyApp::MyClass->new(
person=>MyApp::MyStruct->new(
full_name => 'John',
age_in_years => 39,
),
);
This method may take some additional time to setup but will give you
more flexibility. However, structured constraints are highly
compatible with this method, granting some interesting possibilities
for coercion. Try:
package MyApp::MyClass;
use Moose;
use MyApp::MyStruct;
## It's recommended your type declarations live in a separate class in order
## to promote reusability and clarity. Inlined here for brevity.
use MooseX::Types::DateTime qw(DateTime);
use MooseX::Types -declare [qw(MyStruct)];
use MooseX::Types::Moose qw(Str Int);
use MooseX::Types::Structuredqw(Dict);
## Use class_type to create an ISA type constraint if your object doesn't
## inherit from Moose::Object.
class_type 'MyApp::MyStruct';
## Just a shorter version really.
subtype MyStruct,
as 'MyApp::MyStruct';
## Add the coercions.
coerce MyStruct,
from Dict[
full_name=>Str,
age_in_years=>Int
], via {
MyApp::MyStruct->new(%$_);
},
from Dict[
lastname=>Str,
firstname=>Str,
dob=>DateTime
], via {
my $name = $_->{firstname} .' '. $_->{lastname};
my $age = DateTime->now - $_->{dob};
MyApp::MyStruct->new(
full_name=>$name,
age_in_years=>$age->years,
);
};
has person => (isa=>MyStruct);
This would allow you to instantiate with something like:
my $obj = MyApp::MyClass->new( person => {
full_name=>'John Napiorkowski',
age_in_years=>39,
});
Or even:
my $obj = MyApp::MyClass->new( person => {
lastname=>'John',
firstname=>'Napiorkowski',
dob=>DateTime->new(year=>1969),
});
If you are not familiar with how coercions work, check out the Moose
cookbook entry Moose::Cookbook::Recipe5 for an explanation. The
section "Coercions" has additional examples and discussion.
Subtyping a Structured type constraint
You need to exercise some care when you try to subtype a structured
type as in this example:
subtype Person,
as Dict[name => Str];
subtype FriendlyPerson,
as Person[
name => Str,
total_friends => Int,
];
This will actually work BUT you have to take care that the subtype has
a structure that does not contradict the structure of it's parent. For
now the above works, but I will clarify the syntax for this at a future
point, so it's recommended to avoid (should not really be needed so
much anyway). For now this is supported in an EXPERIMENTAL way. Your
thoughts, test cases and patches are welcomed for discussion. If you
find a good use for this, please let me know.
Coercions
Coercions currently work for 'one level' deep. That is you can do:
subtype Person,
as Dict[
name => Str,
age => Int
];
subtype Fullname,
as Dict[
first => Str,
last => Str
];
coerce Person,
## Coerce an object of a particular class
from BlessedPersonObject, via {
+{
name=>$_->name,
age=>$_->age,
};
},
## Coerce from [$name, $age]
from ArrayRef, via {
+{
name=>$_->[0],
age=>$_->[1],
},
},
## Coerce from {fullname=>{first=>...,last=>...}, dob=>$DateTimeObject}
from Dict[fullname=>Fullname, dob=>DateTime], via {
my $age = $_->dob - DateTime->now;
my $firstn = $_->{fullname}->{first};
my $lastn = $_->{fullname}->{last}
+{
name => $_->{fullname}->{first} .' '. ,
age =>$age->years
}
};
And that should just work as expected. However, if there are any
'inner' coercions, such as a coercion on 'Fullname' or on 'DateTime',
that coercion won't currently get activated.
Please see the test '07-coerce.t' for a more detailed example.
Discussion on extending coercions to support this welcome on the Moose
development channel or mailing list.
Recursion
Newer versions of MooseX::Types support recursive type constraints.
That is you can include a type constraint as a contained type
constraint of itself. For example:
subtype Person,
as Dict[
name=>Str,
friends=>Optional[
ArrayRef[Person]
],
];
This would declare a Person subtype that contains a name and an
optional ArrayRef of Persons who are friends as in:
{
name => 'Mike',
friends => [
{ name => 'John' },
{ name => 'Vincent' },
{
name => 'Tracey',
friends => [
{ name => 'Stephenie' },
{ name => 'Ilya' },
],
},
],
};
Please take care to make sure the recursion node is either Optional, or
declare a Union with an non recursive option such as:
subtype Value
as Tuple[
Str,
Str|Tuple,
];
Which validates:
[
'Hello', [
'World', [
'Is', [
'Getting',
'Old',
],
],
],
];
Otherwise you will define a subtype thatis impossible to validate since
it is infinitely recursive. For more information about defining
recursive types, please see the documentation in MooseX::Types and the
test cases.
TYPE CONSTRAINTS
This type library defines the following constraints.
Tuple[@constraints]
This defines an ArrayRef based constraint which allows you to validate
a specific list of contained constraints. For example:
Tuple[Int,Str]; ## Validates [1,'hello']
Tuple[Str|Object, Int]; ## Validates ['hello', 1] or [$object, 2]
The Values of @constraints should ideally be MooseX::Types declared
type constraints. We do support 'old style' Moose string based
constraints to a limited degree but these string type constraints are
considered deprecated. There will be limited support for bugs
resulting from mixing string and MooseX::Types in your structures. If
you encounter such a bug and really need it fixed, we will required a
detailed test case at the minimum.
Dict[%constraints]
This defines a HashRef based constraint which allowed you to validate a
specific hashref. For example:
Dict[name=>Str, age=>Int]; ## Validates {name=>'John', age=>39}
The keys in %constraints follow the same rules as @constraints in the
above section.
Map[ $key_constraint, $value_constraint ]
This defines a HashRef based constraint in which both the keys and
values are required to meet certain constraints. For example, to map
hostnames to IP addresses, you might say:
Map[ HostName, IPAddress ]
The type constraint would only be met if every key was a valid HostName
and every value was a valid IPAddress.
Optional[$constraint]
This is primarily a helper constraint for Dict and Tuple type
constraints. What this allows is for you to assert that a given type
constraint is allowed to be null (but NOT undefined). If the value is
null, then the type constraint passes but if the value is defined it
must validate against the type constraint. This makes it easy to make
a Dict where one or more of the keys doesn't have to exist or a tuple
where some of the values are not required. For example:
subtype Name() => as Dict[
first=>Str,
last=>Str,
middle=>Optional[Str],
];
Creates a constraint that validates against a hashref with the keys
'first' and 'last' being strings and required while an optional key
'middle' is must be a string if it appears but doesn't have to appear.
So in this case both the following are valid:
{first=>'John', middle=>'James', last=>'Napiorkowski'}
{first=>'Vanessa', last=>'Li'}
If you use the 'Maybe' type constraint instead, your values will also
validate against 'undef', which may be incorrect for you.
EXPORTABLE SUBROUTINES
This type library makes available for export the following subroutines
slurpy
Structured type constraints by their nature are closed; that is
validation will depend on an exact match between your structure
definition and the arguments to be checked. Sometimes you might wish
for a slightly looser amount of validation. For example, you may wish
to validate the first 3 elements of an array reference and allow for an
arbitrary number of additional elements. At first thought you might
think you could do it this way:
# I want to validate stuff like: [1,"hello", $obj, 2,3,4,5,6,...]
subtype AllowTailingArgs,
as Tuple[
Int,
Str,
Object,
ArrayRef[Int],
];
However what this will actually validate are structures like this:
[10,"Hello", $obj, [11,12,13,...] ]; # Notice element 4 is an ArrayRef
In order to allow structured validation of, "and then some", arguments,
you can use the "slurpy" method against a type constraint. For
example:
use MooseX::Types::Structured qw(Tuple slurpy);
subtype AllowTailingArgs,
as Tuple[
Int,
Str,
Object,
slurpy ArrayRef[Int],
];
This will now work as expected, validating ArrayRef structures such as:
[1,"hello", $obj, 2,3,4,5,6,...]
A few caveats apply. First, the slurpy type constraint must be the
last one in the list of type constraint parameters. Second, the parent
type of the slurpy type constraint must match that of the containing
type constraint. That means that a Tuple can allow a slurpy ArrayRef
(or children of ArrayRefs, including another Tuple) and a Dict can
allow a slurpy HashRef (or children/subtypes of HashRef, also including
other Dict constraints).
Please note the the technical way this works 'under the hood' is that
the slurpy keyword transforms the target type constraint into a
coderef. Please do not try to create your own custom coderefs; always
use the slurpy method. The underlying technology may change in the
future but the slurpy keyword will be supported.
ERROR MESSAGES
Error reporting has been improved to return more useful debugging
messages. Now I will stringify the incoming check value with
Devel::PartialDump so that you can see the actual structure that is
tripping up validation. Also, I report the 'internal' validation
error, so that if a particular element inside the Structured Type is
failing validation, you will see that. There's a limit to how deep
this internal reporting goes, but you shouldn't see any of the "failed
with ARRAY(XXXXXX)" that we got with earlier versions of this module.
This support is continuing to expand, so it's best to use these
messages for debugging purposes and not for creating messages that
'escape into the wild' such as error messages sent to the user.
Please see the test '12-error.t' for a more lengthy example. Your
thoughts and preferable tests or code patches very welcome!
EXAMPLES
Here are some additional example usage for structured types. All
examples can be found also in the 't/examples.t' test. Your
contributions are also welcomed.
Normalize a HashRef
You need a hashref to conform to a canonical structure but are required
accept a bunch of different incoming structures. You can normalize
using the Dict type constraint and coercions. This example also shows
structured types mixed which other MooseX::Types libraries.
package Test::MooseX::Meta::TypeConstraint::Structured::Examples::Normalize;
use Moose;
use DateTime;
use MooseX::Types::Structured qw(Dict Tuple);
use MooseX::Types::DateTime qw(DateTime);
use MooseX::Types::Moose qw(Int Str Object);
use MooseX::Types -declare => [qw(Name Age Person)];
subtype Person,
as Dict[
name=>Str,
age=>Int,
];
coerce Person,
from Dict[
first=>Str,
last=>Str,
years=>Int,
], via { +{
name => "$_->{first} $_->{last}",
age => $_->{years},
}},
from Dict[
fullname=>Dict[
last=>Str,
first=>Str,
],
dob=>DateTime,
],
## DateTime needs to be inside of single quotes here to disambiguate the
## class package from the DataTime type constraint imported via the
## line "use MooseX::Types::DateTime qw(DateTime);"
via { +{
name => "$_->{fullname}{first} $_->{fullname}{last}",
age => ($_->{dob} - 'DateTime'->now)->years,
}};
has person => (is=>'rw', isa=>Person, coerce=>1);
And now you can instantiate with all the following:
__PACKAGE__->new(
person=>{
name=>'John Napiorkowski',
age=>39,
},
);
__PACKAGE__->new(
person=>{
first=>'John',
last=>'Napiorkowski',
years=>39,
},
);
__PACKAGE__->new(
person=>{
fullname => {
first=>'John',
last=>'Napiorkowski'
},
dob => 'DateTime'->new(
year=>1969,
month=>2,
day=>13
),
},
);
This technique is a way to support various ways to instantiate your
class in a clean and declarative way.
SEE ALSO
The following modules or resources may be of interest.
Moose, MooseX::Types, Moose::Meta::TypeConstraint,
MooseX::Meta::TypeConstraint::Structured
AUTHORS
· John Napiorkowski <jjnapiork@cpan.org>
· Florian Ragwitz <rafl@debian.org>
· Yuval Kogman <nothingmuch@woobling.org>
· Tomas Doran <bobtfish@bobtfish.net>
· Robert Sedlacek <rs@474.at>
COPYRIGHT AND LICENSE
This software is copyright (c) 2011 by John Napiorkowski.
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 v5.14.1 2011-10-03 MooseX::Types::Structured(3)
