MooseX::Types::Parameterizable - Create your own Parameterizable Types.
SYNOPSIS
- Within your MooseX::Types declared library module:
+ The follow is example usage.
+ package Test::MooseX::Types::Parameterizable::Synopsis;
+
+ use Moose;
use MooseX::Types::Parameterizable qw(Parameterizable);
-
- subtype Set,
- as class_type("Set::Scalar");
+ use MooseX::Types::Moose qw(Str Int ArrayRef);
+ use MooseX::Types -declare=>[qw(Varchar)];
- subtype UniqueInt,
- as Parameterizable[Int, Set],
- where {
- my ($int, $set) = @_;
- return !$set->has($int);
- };
-
- subtype PositiveSet,
- as Set,
- where {
- my ($set) = @_;
- return !grep {$_ <0 } $set->members;
- };
-
- subtype PositiveUniqueInt,
- as UniqueInt[PositiveSet];
-
- my $set = Set::Scalar->new(1,2,3);
+ Create a type constraint that is similar to SQL Varchar type.
- UniqueInt([$set])->check(100); ## Okay, 100 isn't in (1,2,3)
- UniqueInt([$set])->check(-99); ## Okay, -99 isn't in (1,2,3)
- UniqueInt([$set])->check(2); ## Not OK, 2 is in (1,2,3)
-
- PositiveUniqueInt([$set])->check(100); ## Okay, 100 isn't in (1,2,3)
- PositiveUniqueInt([$set])->check(-99); ## Not OK, -99 not Positive Int
- PositiveUniqueInt([$set])->check(2); ## Not OK, 2 is in (1,2,3)
-
- my $negative_set = Set::Scalar->new(-1,-2,-3);
-
- UniqueInt([$negative_set])->check(100); ## Throws exception
+ subtype Varchar,
+ as Parameterizable[Str,Int],
+ where {
+ my($string, $int) = @_;
+ $int >= length($string) ? 1:0;
+ },
+ message { "'$_' is too long" };
+
+ Coerce an ArrayRef to a string via concatenation.
+
+ coerce Varchar,
+ from ArrayRef,
+ via {
+ my ($arrayref, $int) = @_;
+ join('', @$arrayref);
+ };
+
+ has 'varchar_five' => (isa=>Varchar[5], is=>'ro', coerce=>1);
+ has 'varchar_ten' => (isa=>Varchar[10], is=>'ro');
+
+ Object created since attributes are valid
+
+ my $object1 = __PACKAGE__->new(
+ varchar_five => '1234',
+ varchar_ten => '123456789',
+ );
+
+ Dies with an invalid constraint for 'varchar_five'
+
+ my $object2 = __PACKAGE__->new(
+ varchar_five => '12345678', ## too long!
+ varchar_ten => '123456789',
+ );
+
+ varchar_five coerces as expected
+
+ my $object3 = __PACKAGE__->new(
+ varchar_five => [qw/aa bb/], ## coerces to "aabb"
+ varchar_ten => '123456789',
+ );
+
+ See t/05-pod-examples.t for runnable versions of all POD code
DESCRIPTION
A MooseX::Types library for creating parameterizable types. A
parameterizable type constraint for all intents and uses is a subclass
- of a parent type, but adds a secondary type parameter which is available
- to constraint callbacks (such as inside the 'where' clause) or in the
- coercions.
-
- This allows you to create a type that has additional runtime advice,
- such as a set of numbers within which another number must be unique, or
- allowable ranges for a integer, such as in:
-
- subtype Range,
- as Dict[max=>Int, min=>Int],
- where {
- my ($range) = @_;
- return $range->{max} > $range->{min};
- };
-
- subtype RangedInt,
- as Parameterizable[Int, Range],
- where {
- my ($value, $range) = @_;
- return ($value >= $range->{min} &&
- $value <= $range->{max});
- };
-
- RangedInt([{min=>10,max=>100}])->check(50); ## OK
- RangedInt([{min=>50, max=>75}])->check(99); ## Not OK, 99 exceeds max
-
- This throws a hard Moose exception. You'll need to capture it in an eval
- or related exception catching system (see TryCatch).
-
- RangedInt([{min=>99, max=>10}])->check(10); ## Not OK, not a valid Range!
+ of a parent type, but adds additional type parameters which are
+ available to constraint callbacks (such as inside the 'where' clause of
+ a type constraint definition) or in the coercions.
+
+ If you have Moose experience, you probably are familiar with the builtin
+ parameterizable type constraints 'ArrayRef' and 'HashRef'. This type
+ constraint lets you generate your own versions of parameterized
+ constraints that work similarly. See Moose::Util::TypeConstraints for
+ more.
+
+ Using this type constraint, you can generate new type constraints that
+ have additional runtime advice, such as being able to specify maximum
+ and minimum values for an Int (integer) type constraint:
+
+ subtype Range,
+ as Dict[max=>Int, min=>Int],
+ where {
+ my ($range) = @_;
+ return $range->{max} > $range->{min};
+ };
+
+ subtype RangedInt,
+ as Parameterizable[Int, Range],
+ where {
+ my ($value, $range) = @_;
+ return ($value >= $range->{min} &&
+ $value <= $range->{max});
+ };
+
+ RangedInt([{min=>10,max=>100}])->check(50); ## OK
+ RangedInt([{min=>50, max=>75}])->check(99); ## Not OK, exceeds max
+
+ The type parameter must be valid against the type constraint given. If
+ you pass an invalid value this throws a hard Moose exception. You'll
+ need to capture it in an eval or related exception catching system (see
+ TryCatch or <Try::Tiny>.) For example the following would throw a hard
+ error (and not just return false)
+
+ RangedInt([{min=>99, max=>10}])->check(10); ## Not OK, not a valid Range!
If you can't accept a hard exception here, you'll need to test the
constraining values first, as in:
- my $range = {min=>99, max=>10};
- if(my $err = Range->validate($range)) {
- ## Handle #$err
- } else {
- RangedInt($range)->check(99);
- }
+ my $range = {min=>99, max=>10};
+ if(my $err = Range->validate($range)) {
+ ## Handle #$err
+ } else {
+ RangedInt($range)->check(99);
+ }
Please note that for ArrayRef or HashRef parameterizable type
constraints, as in the example above, as a convenience we automatically
ref the incoming type parameters, so that the above could also be
written as:
- RangedInt([min=>10,max=>100])->check(50); ## OK
- RangedInt([min=>50, max=>75])->check(99); ## Not OK, 99 exceeds max
- RangedInt([min=>99, max=>10])->check(10); ## Exception, not a valid Range!
+ RangedInt([min=>10,max=>100])->check(50); ## OK
+ RangedInt([min=>50, max=>75])->check(99); ## Not OK, exceeds max
+ RangedInt([min=>99, max=>10])->check(10); ## Exception, not valid Range
This is the preferred syntax, as it improve readability and adds to the
conciseness of your type constraint declarations. An exception wil be
thrown if your type parameters don't match the required reference type.
- Also not that if you 'chain' parameterization results with a method call
- like:
+ Also note that if you 'chain' parameterization results with a method
+ call like:
- TypeConstraint([$ob])->method;
+ TypeConstraint([$ob])->method;
You need to have the "(...)" around the ArrayRef in the Type Constraint
- parameters. This seems to have something to do with the precendent level
- of "->". Patches or thoughts welcomed. You only need to do this in the
- above case which I imagine is not a very common case.
-
- ==head2 Subtyping a Parameterizable type constraints
+ parameters. You can skip the wrapping parenthesis in the most common
+ cases, such as when you use the type constraint in the options section
+ of a Moose attribute declaration, or when defining type libraries.
+ Subtyping a Parameterizable type constraints
When subclassing a parameterizable type you must be careful to match
either the required type parameter type constraint, or if
re-parameterizing, the new type constraints are a subtype of the parent.
For example:
- subtype RangedInt,
- as Parameterizable[Int, Range],
- where {
- my ($value, $range) = @_;
- return ($value >= $range->{min} &&
- $value =< $range->{max});
- };
+ subtype RangedInt,
+ as Parameterizable[Int, Range],
+ where {
+ my ($value, $range) = @_;
+ return ($value >= $range->{min} &&
+ $value =< $range->{max});
+ };
Example subtype with additional constraints:
- subtype PositiveRangedInt,
- as RangedInt,
- where {
- shift >= 0;
- };
-
- Or you could have done the following instead:
-
- ## Subtype of Int for positive numbers
- subtype PositiveInt,
- as Int,
- where {
- my ($value, $range) = @_;
- return $value >= 0;
- };
-
- ## subtype Range to re-parameterize Range with subtypes
- subtype PositiveRange,
- as Range[max=>PositiveInt, min=>PositiveInt];
-
- ## create subtype via reparameterizing
- subtype PositiveRangedInt,
- as RangedInt[PositiveRange];
+ subtype PositiveRangedInt,
+ as RangedInt,
+ where {
+ shift >= 0;
+ };
+
+ In this case you'd now have a parameterizable type constraint called
+ which would work like:
+
+ Test::More::ok PositiveRangedInt([{min=>-10, max=>75}])->check(5);
+ Test::More::ok !PositiveRangedInt([{min=>-10, max=>75}])->check(-5);
+
+ Of course the above is somewhat counter-intuitive to the reader, since
+ we have defined our 'RangedInt' in such as way as to let you declare
+ negative ranges. For the moment each type constraint rule is apply
+ without knowledge of any other rule, nor can a rule 'inform' existing
+ rules. This is a limitation of the current system. However, you could
+ instead do the following:
+
+ ## Subtype of Int for positive numbers
+ subtype PositiveInt,
+ as Int,
+ where {
+ my ($value, $range) = @_;
+ return $value >= 0;
+ };
+
+ ## subtype Range to re-parameterize Range with subtypes
+ subtype PositiveRange,
+ as Range[max=>PositiveInt, min=>PositiveInt];
+
+ ## create subtype via reparameterizing
+ subtype PositiveRangedInt,
+ as RangedInt[PositiveRange];
+
+ This would constrain values in the same way as the previous type
+ constraint but have the bonus that you'd throw a hard exception if you
+ try to use an incorrect range:
+
+ Test::More::ok PositiveRangedInt([{min=>10, max=>75}])->check(15); ## OK
+ Test::More::ok !PositiveRangedInt([{min=>-10, max=>75}])->check(-5); ## Dies
Notice how re-parameterizing the parameterizable type 'RangedInt' works
slightly differently from re-parameterizing 'PositiveRange' Although it
initially takes two type constraint values to declare a parameterizable
type, should you wish to later re-parameterize it, you only use a
- subtype of the second type parameter (the parameterizable type
- constraint) since the first type constraint sets the parent type for the
- parameterizable type. In other words, given the example above, a type
- constraint of 'RangedInt' would have a parent of 'Int', not
- 'Parameterizable' and for all intends and uses you could stick it
- wherever you'd need an Int.
-
- subtype NameAge,
- as Tuple[Str, Int];
-
- ## re-parameterized subtypes of NameAge containing a Parameterizable Int
- subtype NameBetween18and35Age,
- as NameAge[
- Str,
- PositiveRangedInt[min=>18,max=>35],
- ];
-
- One caveat is that you can't stick an unparameterized parameterizable
- type inside a structure, such as MooseX::Types::Structured since that
- would require the ability to convert a 'containing' type constraint into
- a parameterizable type, which is a capacity we current don't have.
+ subtype of the extra type parameter (the parameterizable type
+ constraints) since the first type constraint sets the parent type for
+ the parameterizable type.
+
+ In other words, given the example above, a type constraint of
+ 'RangedInt' would have a parent of 'Int', not 'Parameterizable' and for
+ all intends and uses you could stick it wherever you'd need an Int.
Coercions
- Parameterizable types have some limited support for coercions. Several
- things must be kept in mind. The first is that the coercion targets the
- type constraint which is being made parameterizable, Not the
- parameterizable type. So for example if you create a Parameterizable
- type like:
-
- subtype RequiredAgeInYears,
- as Int;
-
- subtype PersonOverAge,
- as Parameterizable[Person, RequiredAgeInYears]
- where {
- my ($person, $required_years_old) = @_;
- return $person->years_old > $required_years_old;
- }
-
- This would validate the following:
-
- my $person = Person->new(age=>35);
- PersonOverAge([18])->check($person);
-
- You can then apply the following coercion
-
- coerce PersonOverAge,
- from Dict[age=>int],
- via {Person->new(%$_)},
- from Int,
- via {Person->new(age=>$_)};
-
- This coercion would then apply to all the following:
-
- PersonOverAge([18])->check(30); ## via the Int coercion
- PersonOverAge([18])->check({age=>50}); ## via the Dict coercion
-
- However, you are not allowed to place coercions on parameterizable types
- that have had their constraining value filled, nor subtypes of such. For
- example:
-
- coerce PersonOverAge[18],
- from DateTime,
- via {$_->years};
-
- That would generate a hard exception. This is a limitation for now until
- I can devise a smarter way to cache the generated type constraints.
- However, I doubt it will be a significant limitation, since the general
- use case is supported.
-
- Lastly, the constraining value is available in the coercion in much the
- same way it is available to the constraint.
-
- ## Create a type constraint where a Person must be in the set
- subtype PersonInSet,
- as Parameterizable[Person, PersonSet],
- where {
- my ($person, $person_set) = @_;
- $person_set->find($person);
- }
-
- coerce PersonInSet,
- from HashRef,
- via {
- my ($hashref, $person_set) = @_;
- return $person_set->create($hash_ref);
- };
+ A type coerction is a rule that allows you to transform one type from
+ one or more other types. Please see Moose::Cookbook::Basics::Recipe5 for
+ an example of type coercions if you are not familiar with the subject.
+
+ MooseX::Types::Parameterizable support type coercions in all the ways
+ you would expect. In addition, it also supports a limited form of type
+ coercion inheritance. Generally speaking, type constraints don't inherit
+ coercions since this would rapidly become confusing. However, since your
+ parameterizable type is intended to become parameterized in order to be
+ useful, we support inheriting from a 'base' parameterizable type
+ constraint to its 'child' parameterized sub types.
+
+ For the purposes of this discussion, a parameterizable type is a subtype
+ created when you say, "as Parameterizable[..." in your sub type
+ declaration. For example
+
+ subtype Varchar,
+ as Parameterizable[Str, Int],
+ where {
+ my($string, $int) = @_;
+ $int >= length($string) ? 1:0;
+ },
+ message { "'$_' is too long" };
+
+ This is the </SYNOPSIS> example, which creates a new parameterizable
+ subtype of Str which takes a single type parameter which must be an Int.
+ This Int is used to constrain the allowed length of the Str value.
+
+ Now, this new sub type, "Varchar", is parameterizable since it can take
+ a type parameter. We can apply some coercions to it:
+
+ coerce Varchar,
+ from Object,
+ via { "$_"; }, ## stringify the object
+ from ArrayRef,
+ via { join '',@$_ }; ## convert array to string
+
+ This parameterizable subtype, "Varchar" itself is something you'd never
+ use directly to constraint a value. In other words you'd never do
+ something like:
+
+ has name => (isa=>Varchar, ...)
+
+ You are going to do this:
+
+ has name => (isa=>Varchar[40], ...)
+
+ Which is actually useful. However, "Varchar[40]" is a parameterized
+ type, it is a subtype of the parameterizable "Varchar" and it inherits
+ coercions from its parent. This may be a bit surprising to Moose
+ developers, but I believe this is the actual desired behavior.
+
+ You can of course add new coercions to a subtype of a parameterizable
+ type:
+
+ subtype MySpecialVarchar,
+ as Varchar;
+
+ coerce MySpecialVarchar,
+ from ...
+
+ In which case this new parameterizable type would NOT inherit coercions
+ from it's parent parameterizable type (Varchar). This is done in keeping
+ with how generally speaking Moose type constraints avoid complicated
+ coercion inheritance schemes, however I am open to discussion if there
+ are valid use cases.
+
+ NOTE: One thing you can't do is add a coercion to an already
+ parameterized type. Currently the following would throw a hard error:
+
+ subtype 40CharStr,
+ as Varchar[40];
+
+ coerce 40CharStr, ... # BANG!
+
+ This limitation is enforced since generally we expect coercions on the
+ parent. However if good use cases arise we may lift this in the future.
+
+ In general we are trying to take a conservative approach that keeps in
+ line with how most Moose authors expect type constraints to work.
Recursion
- TBD
+ TBD - Needs a use case... Anyone?
TYPE CONSTRAINTS
This type library defines the following constraints.
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