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# NAME
Type::Alias - type alias for type constraints
# SYNOPSIS
```perl
use Type::Alias -alias => [qw(ID User UserData)], -fun => [qw(List)];
use Types::Standard -types;
type ID => Str;
type User => {
id => ID,
name => Str,
age => Int,
};
type List => sub {
my ($R) = @_;
$R ? ArrayRef[$R] : ArrayRef;
};
type UserData => List[User] | User;
UserData->check([
{ id => '1', name => 'foo', age => 20 },
{ id => '2', name => 'bar', age => 30 },
]); # OK
UserData->check(
{ id => '1', name => 'foo', age => 20 },
); # OK
# Internally List[User] is equivalent to the following type:
#
# ArrayRef[
# Dict[
# age=>Int,
# id=>Str,
# name=>Str
# ]
# ]
```
# DESCRIPTION
Type::Alias creates type aliases and type functions for existing type constraints such as Type::Tiny, Moose, Mouse. The aim of this module is to enhance the reusability of types and make it easier to express types.
## IMPORT OPTIONS
### -alias
`-alias` is an array reference that defines type aliases. The default is `[]`.
```perl
use Type::Alias -alias => [qw(ID User)];
type ID => Str;
type User => {
id => ID,
name => Str,
age => Int,
};
```
### -fun
`-fun` is an array reference that defines type functions. The default is `[]`.
```perl
use Type::Alias -fun => [qw(List)];
type List => sub($R) {
$R ? ArrayRef[$R] : ArrayRef;
};
```
### type
The `type` option is used to configure the type function that defines type aliases and type functions.
```perl
# Rename type function:
use Type::Alias type => { -as => 'mytype' };
mytype ID => Str; # declare type alias
```
## EXPORTED FUNCTIONS
### type($alias\_name, $type\_args)
`type` is a function that defines type alias and type function.
It recursively generates type constraints based on `$type_args`.
Given a type constraint in `$type_args`, it returns the type constraint as is.
Type::Alias treats objects with `check` and `get_message` methods as type constraints.
```perl
type ID => Str;
ID->check('foo'); # OK
```
Internally `ID` is equivalent to the following type:
```perl
sub ID() { Str }
```
Given a hash reference in `$type_args`, it returns the type constraint defined by Type::Tiny's Dict type.
```perl
type Point => {
x => Int,
y => Int,
};
Point->check({
x => 1,
y => 2
}); # OK
```
Internally `Point` is equivalent to the following type:
```perl
sub Point() { Dict[x=>Int,y=>Int] }
```
Given an array reference in `$type_args`, it returns the type constraint defined by Type::Tiny's Tuple type.
```perl
type Option => [Str, Int];
Option->check('foo', 1); # OK
```
Internally `Option` is equivalent to the following type:
```perl
sub Option() { Tuple[Str,Int] }
```
Given a code reference in `$type_args`, it defines a type function that accepts a type constraint as an argument and return the type constraint.
```perl
type List => sub($R) {
$R ? ArrayRef[$R] : ArrayRef;
};
type Points => List[{ x => Int, y => Int }];
Points->check([
{ x => 1, y => 2 },
{ x => 3, y => 4 },
]); # OK
```
Internally `List` is equivalent to the following type:
```perl
sub List :prototype(;$) {
my @args = map { Type::Alias::to_type($_) } @{$_[0]};
sub($R) {
$R ? ArrayRef[$R] : ArrayRef;
}->(@args);
}
```
And `Points` is equivalent to the following type:
```perl
sub Points() { List[Dict[x=>Int,y=>Int]] }
```
# COOKBOOK
## Exporter
Type::Alias is designed to be used with Exporter. The following is an example of using Type::Alias with Exporter.
```perl
package MyService {
use Exporter 'import';
our @EXPORT_OK = qw(hello Message);
use Type::Alias -alias => [qw(Message)];
use Types::Common -types;
type Message => StrLength[1, 100];
sub hello { ... }
}
package MyApp {
use MyService qw(Message);
Message->check('World!');
}
```
## Class builders
Type::Alias is designed to be used with class builders such as [Moose](https://metacpan.org/pod/Moose), [Moo](https://metacpan.org/pod/Moo) and [Mouse](https://metacpan.org/pod/Mouse).
```perl
package Sample {
use Moose;
use Exporter 'import';
our @EXPORT_OK = qw( UserName );
use Type::Alias -alias => [qw( UserName )];
use Types::Standard qw( Str );
type UserName => Str & sub { length $_ > 1 };
has 'name' => (is => 'rw', isa => UserName);
}
package MyApp {
use Sample qw( UserName );
my $sample = Sample->new(name => 'hello');
$sample->hello; # => 'hello'
$sample->hello(''); # ERROR!
UserName->check('hello'); # OK
}
```
## Validation modules
Type::Alias is designed to be used with validation modules such as [Type::Params](https://metacpan.org/pod/Type%3A%3AParams), [Smart::Args::TypeTiny](https://metacpan.org/pod/Smart%3A%3AArgs%3A%3ATypeTiny) and [Data::Validator](https://metacpan.org/pod/Data%3A%3AValidator):
```perl
use Type::Alias -alias => [qw( Message )];
use Types::Standard qw( Str );
use Type::Params -sigs;
type Message => Str & sub { length($_) > 1 };
signature_for hello => (
positional => [ Message ],
);
sub hello {
my ($message) = @_;
return "HELLO " . $message;
}
hello('World') # => 'HELLO World';
hello('') # => Error!
```
### NOTE
[Function::Parameters](https://metacpan.org/pod/Function%3A%3AParameters) works using type aliases from outside.
```perl
package Sample {
use Exporter 'import';
our @EXPORT_OK = qw(User);
use Type::Alias -alias => [qw(User)];
use Types::Standard -types;
type User => {
name => Str,
};
}
use Types::Standard -types;
use Function::Parameters;
use Sample qw(User);
fun hello (User $user) {
return "Hello, $user->{name}!";
}
hello({ name => 'foo' }) # => 'Hello, foo!';
```
However, if you write a type alias inline as follows, the current implementation will not work.
```perl
use Type::Alias -alias => [qw(Gorilla)];
type Gorilla => Dict[ name => Str ];
fun ooh(Gorilla $user) { # => ERROR: type Gorilla is not defined at compile time
return "ooh ooh, $user->{name}!";
}
ooh({ name => 'gorilla' }) # => 'ooh ooh, gorilla!';
```
# SEE ALSO
[Type::Tiny](https://metacpan.org/pod/Type%3A%3ATiny)
# LICENSE
Copyright (C) kobaken.
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
# AUTHOR
kobaken <kfly@cpan.org>