NAME

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

SYNOPSIS

Using via Types::Standard:

  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' ],
  );

BUGS

Please report any bugs to <https://github.com/tobyink/p5-type-tiny/issues>.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

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.