Type::Tiny::Manual::Libraries - how to build a type library with Type::Tiny, Type::Library and Type::Utils |
Type::Tiny::Manual::Libraries - how to build a type library with Type::Tiny, Type::Library and Type::Utils
A type library is a collection of type constraints, optionally with coercions.
The following is an example type library:
package Example::Types; use Type::Library -base, -declare => qw( Datetime DatetimeHash EpochHash ); use Type::Utils -all; use Types::Standard -types; class_type Datetime, { class => "DateTime" }; declare DatetimeHash, as Dict[ year => Int, month => Optional[ Int ], day => Optional[ Int ], hour => Optional[ Int ], minute => Optional[ Int ], second => Optional[ Int ], nanosecond => Optional[ Int ], time_zone => Optional[ Str ], ]; declare EpochHash, as Dict[ epoch => Int ]; coerce Datetime, from Int, via { "DateTime"->from_epoch(epoch => $_) }, from Undef, via { "DateTime"->now }, from DatetimeHash, via { "DateTime"->new(%$_) }, from EpochHash, via { "DateTime"->from_epoch(%$_) }; 1;
Here's a line by line description of what's going on in the type library.
package Example::Types;
Type libraries are packages. It is recommended that re-usable type libraries
be given a name in the Types::*
namespace. For application-specific
type libraries, assuming your application's namespace is MyApp::*
then
name the type library MyApp::Types
, or if more than one is needed, use
the MyApp::Types::*
namespace.
use Type::Library -base, -declare => qw( Datetime DatetimeHash EpochHash );
The -base
part is used to establish inheritance. It makes
Example::Types
a child class of Type::Library
.
Declaring the types we're going to define ahead of their definition allows us to use them as barewords later on. (Note that in code which uses our type library, the types will always be available as barewords. The declaration above just allows us to use them within the library itself.)
use Type::Utils -all;
Imports some utility functions from the Type::Utils manpage. These will be useful for defining our types and the relationships between them.
use Types::Standard -types;
Here we import a standard set of type constraints from the Types::Standard manpage. There is no need to do this, but it's often helpful to have a base set of types which we can define our own in terms of.
Note that although we've imported the types to be able to use in our library,
we haven't added the types to our library. We've imported Str
, but other
people won't be able to re-import Str
from our library. If you actually
want your library to extend another library, do this instead:
BEGIN { extends "Types::AnotherLibrary" };
(Note: if your code breaks here when you upgrade from version 0.006 or below, saying that the 'extends' keyword has not been declared, just add '-all' after use Type::Utils.)
OK, now we're ready to declare a few types.
class_type Datetime, { class => "DateTime" };
This creates a type constraint named ``Datetime'' which is all objects blessed into the DateTime package. Because this type constraint is not anonymous (it has a name), it will be automagically installed into the type library.
The next two statements declare two further types constraints, using type
constraints from the Types::Standard library. Let's look at EpochHash
in
more detail. This is a hashref with one key called ``epoch'' and a value which
is an integer.
declare EpochHash, as Dict[ epoch => Int ];
EpochHash
inherits from the Dict
type defined in Types::Standard. It
equally could have been defined as:
declare EpochHash, as HashRef[Int], where { scalar(keys(%$_))==1 and exists $_->{epoch} };
Or even:
declare EpochHash, where { ref($_) eq "HASH" and scalar(keys(%$_))==1 and exists $_->{epoch} };
Lastly we set up coercions. It's best to define all your types before you define any coercions.
coerce Datetime, from Int, via { "DateTime"->from_epoch(epoch => $_) }, from Undef, via { "DateTime"->now }, from DatetimeHash, via { "DateTime"->new(%$_) }, from EpochHash, via { "DateTime"->from_epoch(%$_) };
These are simply coderefs that will be fired when you want a Datetime, but are given something else. For more information on coercions, see the Type::Tiny::Manual::Coercions manpage.
Use a custom types library just like you would the Types::Standard manpage:
packge MyClass; use Moose; use DateTime; use Example::Types qw( Datetime ); # import the custom type has 'sometime' => ( is => 'rw', isa => Datetime, coerce => 1, );
Type libraries defined with the Type::Library manpage are also able to export some convenience functions:
use Example::Types qw( is_Datetime to_Datetime assert_Datetime ); my $dt = Foo::get_datetime; unless ( is_Datetime $dt ) { $dt = to_Datetime $dt; } assert_Datetime $dt;
These functions act as shortcuts for:
use Example::Types qw( Datetime ); my $dt = Foo::get_datetime; unless ( Datetime->check($dt) ) { $dt = Datetime->coerce($dt); } Datetime->assert_return($dt);
Pick whichever style you think is clearer!
Type::Library-based libraries provide a shortcut for importing a type constraint along with all its associated convenience functions:
# Shortcut for qw( DateTime is_Datetime to_Datetime assert_Datetime ) # use Example::Types qw( +Datetime );
See the Type::Tiny::Manual manpage for other ways to make use of type libraries.
It is sometimes nice to be able to emit a more useful error message than the standard:
Value "Foo" did not pass type constraint "Bar"
It is possible to define custom error messages for types.
declare MediumInteger, as Integer, where { $_ >= 10 and $_ < 20 }, message { return Integer->get_message($_) if !Integer->check($_); return "$_ is too small!" if $_ < 10; return "$_ is so very, very big!"; };
Parameterized type constraints are those that can generate simple child type
constraints by passing parameters to their parameterize
method. For
example, ArrayRef in Types::Standard:
use Types::Standard; my $ArrayRef = Types::Standard::ArrayRef; my $Int = Types::Standard::Int; my $ArrayRef_of_Ints = $ArrayRef->parameterize($Int);
Type libraries provide some convenient sugar for this:
use Types::Standard qw( ArrayRef Int ); my $ArrayRef_of_Ints = ArrayRef[Int];
Unlike Moose which has separate meta classes for parameterizable, parameterized and non-parameterizable type constraints, the Type::Tiny manpage handles all that in one.
To create a parameterizable type constraint, you'll need to pass an extra
named parameter to declare
. Let's imagine that we want to make our earlier
NonEmptyHash
constraint accept a parameter telling it the minimum size of
the hash. For example NonEmptyHash[4]
would need to contain at least
four key-value pairs. Here's how you'd do it:
declare NonEmptyHash, as HashLike, where { scalar values %$_ }, inline_as { my ($constraint, $varname) = @_; return sprintf( '%s and scalar values %%{%s}', $constraint->parent->inline_check($varname), $varname, ); }, # Generate a new "where" coderef... constraint_generator => sub { my ($minimum) = @_; die "parameter must be positive" unless int($minimum) > 0; return sub { scalar(values(%$_)) >= int($minimum); }; }, # Generate a new "inline_as" coderef... inline_generator => sub { my ($minimum) = @_; return sub { my ($constraint, $varname) = @_; return sprintf( '%s and scalar(values(%%{%s})) >= %d', $constraint->parent->inline_check($varname), $varname, $minimum, ); }; };
Some type libraries on CPAN:
Toby Inkster <tobyink@cpan.org>.
This software is copyright (c) 2013-2014 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
THIS PACKAGE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
Type::Tiny::Manual::Libraries - how to build a type library with Type::Tiny, Type::Library and Type::Utils |