Toby Inkster > Return-Type > Return::Type

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NAME ^

Return::Type - specify a return type for a function (optionally with coercion)

SYNOPSIS ^

   use Return::Type;
   use Types::Standard qw(Int);
   
   sub first_item :ReturnType(Int) {
      return $_[0];
   }
   
   my $answer = first_item(42, 43, 44);     # returns 42
   my $pie    = first_item(3.141592);       # throws an error!

DESCRIPTION ^

Return::Type allows you to specify a return type for your subs. Type constraints from any Type::Tiny, MooseX::Types or MouseX::Types type library are supported.

The simple syntax for specifying a type constraint is shown in the "SYNOPSIS". If the attribute is passed a single type constraint as shown, this will be applied to the return value if called in scalar context, and to each item in the returned list if called in list context. (If the sub is called in void context, type constraints are simply ignored.)

It is possible to specify different type constraints for scalar and list context:

   sub foo :ReturnType(scalar => Int, list => HashRef[Num]) {
      if (wantarray) {
         return (pie => 3.141592);
      }
      else {
         return 42;
      }
   }

Note that because type constraint libraries are really aimed at validating scalars, the type constraint for the list is specified as a hashref of numbers and not a hash of numbers! For the purposes of validation against the type constraint, we slurp the returned list into a temporary arrayref or hashref.

For type constraints with coercions, you can also pass the option coerce => 1:

   use Return::Type;
   use Types::Standard qw( Int Num );
   
   # Define a subtype of "Int" at compile time, which can
   # coerce from "Num" by rounding to nearest integer.
   use constant Rounded => Int->plus_coercions(Num, sub { int($_) });
   
   sub first_item :ReturnType(scalar => Rounded, coerce => 1) {
      return $_[0];
   }
   
   my $answer = first_item(42, 43, 44);     # returns 42
   my $pie    = first_item(3.141592);       # returns 3

The options coerce_scalar and coerce_list are also available if you wish to enable coercion only in particular contexts.

Power-user Inferface

Rather than using the :ReturnType attribute, it's possible to wrap a coderef like this:

   my $wrapped = Return::Type->wrap_sub($orig, %options);

The accepted options are scalar, list, coerce, coerce_list, and coerce_scalar, as per the attribute-based interface.

BUGS ^

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Return-Type.

SEE ALSO ^

Attribute::Contract, Sub::Filter, Sub::Contract.

AUTHOR ^

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE ^

This software is copyright (c) 2013 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.

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.

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