Type::Tiny::Duck - type constraints based on the "can" method

NAME SYNOPSIS STATUS DESCRIPTION Attributes Methods Exports BUGS SEE ALSO AUTHOR COPYRIGHT AND LICENCE DISCLAIMER OF WARRANTIES

NAME

Type::Tiny::Duck − type constraints based on the "can" method

package Logger {
use Moo;
use Types::Standard qw( HasMethods Bool );
has debugging => ( is => 'rw', isa => Bool, default => 0 );
has output => ( is => 'ro', isa => HasMethods[ 'print' ] );
sub warn {
my ( $self, $message ) = @_;
$self−>output−>print( "[WARNING] $message\n" );
}
sub debug {
my ( $self, $message ) = @_;
$self−>output−>print( "[DEBUG] $message\n" ) if $self−>debugging;
}
}

Using Type::Tiny::Duck’s export feature:

package Logger {
use Moo;
use Types::Standard qw( Bool );
use Type::Tiny::Duck Printable => [ 'print' ];
has debugging => ( is => 'rw', isa => Bool, default => 0 );
has output => ( is => 'ro', isa => Printable );
sub warn {
my ( $self, $message ) = @_;
$self−>output−>print( "[WARNING] $message\n" );
}
sub debug {
my ( $self, $message ) = @_;
$self−>output−>print( "[DEBUG] $message\n" ) if $self−>debugging;
}
}

Using Type::Tiny::Duck’s object-oriented interface:

package Logger {
use Moo;
use Types::Standard qw( Bool );
use Type::Tiny::Duck;
my $Printable = Type::Type::Duck−>new(
name => 'Printable',
methods => [ 'print' ],
);
has debugging => ( is => 'rw', isa => Bool, default => 0 );
has output => ( is => 'ro', isa => $Printable );
sub warn {
my ( $self, $message ) = @_;
$self−>output−>print( "[WARNING] $message\n" );
}
sub debug {
my ( $self, $message ) = @_;
$self−>output−>print( "[DEBUG] $message\n" ) if $self−>debugging;
}
}

STATUS

This module is covered by the Type-Tiny stability policy.

DESCRIPTION

Type constraints of the general form "{ $_−>can("method") }".

The name refers to the saying, "If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck". Duck typing can be a more flexible way of testing objects than relying on "isa", as it allows people to easily substitute mock objects.

This package inherits from Type::Tiny; see that for most documentation. Major differences are listed below:

Attributes

"methods"

An arrayref of method names.

"constraint"

Unlike Type::Tiny, you cannot pass a constraint coderef to the constructor. Instead rely on the default.

"inlined"

Unlike Type::Tiny, you cannot pass an inlining coderef to the constructor. Instead rely on the default.

"parent"

Parent is always Types::Standard::Object, and cannot be passed to the constructor.

Methods

stringifies_to($constraint)

See Type::Tiny::ConstrainedObject.

numifies_to($constraint)

See Type::Tiny::ConstrainedObject.

"with_attribute_values($attr1 => $constraint1, ...)"

See Type::Tiny::ConstrainedObject.

Exports

Type::Tiny::Duck can be used as an exporter.

use Type::Tiny::Duck HttpClient => [ 'get', 'post' ];

This will export the following functions into your namespace:
"HttpClient"
is_HttpClient( $value )
assert_HttpClient( $value )
to_HttpClient( $value )

Multiple types can be exported at once:

use Type::Tiny::Duck (
HttpClient => [ 'get', 'post' ],
FtpClient => [ 'upload', 'download' ],
);