NAME Scalar::Does - like ref() but useful SYNOPSIS use Scalar::Does qw( -constants ); my $object = bless {}, 'Some::Class'; does($object, 'Some::Class'); # true does($object, '%{}'); # true does($object, HASH); # true does($object, ARRAY); # false DESCRIPTION It has long been noted that Perl would benefit from a `does()` built-in. A check that `ref($thing) eq 'ARRAY'` doesn't allow you to accept an object that uses overloading to provide an array-like interface. Functions `does($scalar, $role)` Checks if a scalar is capable of performing the given role. The following (case-sensitive) roles are predefined: * SCALAR or ${} Checks if the scalar can be used as a scalar reference. Note: this role does not check whether a scalar is a scalar (which is obviously true) but whether it is a reference to another scalar. * ARRAY or @{} Checks if the scalar can be used as an array reference. * HASH or %{} Checks if the scalar can be used as a hash reference. * CODE or &{} Checks if the scalar can be used as a code reference. * GLOB or *{} Checks if the scalar can be used as a glob reference. * REF Checks if the scalar can be used as a ref reference (i.e. a reference to another reference). * LVALUE Checks if the scalar is a reference to a special lvalue (e.g. the result of `substr` or `splice`). * IO or <> Uses IO::Detect to check if the scalar is a filehandle or file-handle-like object. (The `<>` check is slightly looser, allowing objects which overload `<>`, though overloading `<>` well can be a little tricky.) * VSTRING Checks if the scalar is a vstring reference. * FORMAT Checks if the scalar is a format reference. * Regexp or qr Checks if the scalar can be used as a quoted regular expression. * bool Checks if the scalar can be used as a boolean. (It's pretty rare for this to not be true.) * "" Checks if the scalar can be used as a string. (It's pretty rare for this to not be true.) * 0+ Checks if the scalar can be used as a number. (It's pretty rare for this to not be true.) Note that this is far looser than `looks_like_number` from Scalar::Util. For example, an unblessed arrayref can be used as a number (it numifies to its reference address); the string "Hello World" can be used as a number (it numifies to 0). * ~~ Checks if the scalar can be used on the right hand side of a smart match. If the given *role* is blessed, and provides a `check` method, then `does` delegates to that. Otherwise, if the scalar being tested is blessed, then `$scalar->DOES($role)` is called, and `does` returns true if the method call returned true. If the scalar being tested looks like a Perl class name, then `$scalar->DOES($role)` is also called, and the string "0E0" is returned for success, which evaluates to 0 in a numeric context but true in a boolean context. `does($role)` Called with a single argument, tests $_. Yes, this works with lexical $_. given ($object) { when(does ARRAY) { ... } when(does HASH) { ... } } Note: in Scalar::Does 0.007 and below the single-argument form of `does` returned a curried coderef. This was changed in Scalar::Does 0.008. `overloads($scalar, $role)` A function `overloads` (which just checks overloading) is also available. `overloads($role)` Called with a single argument, tests $_. Yes, this works with lexical $_. Note: in Scalar::Does 0.007 and below the single-argument form of `overloads` returned a curried coderef. This was changed in Scalar::Does 0.008. `blessed($scalar)`, `reftype($scalar)`, `looks_like_number($scalar)` For convenience, this module can also re-export these functions from Scalar::Util. `looks_like_number` is generally more useful than `does($scalar, q[0+])`. `make_role $name, where { BLOCK }` Returns an anonymous role object which can be used as a parameter to `does`. The block is arbitrary code which should check whether $_[0] does the role. `where { BLOCK }` Syntactic sugar for `make_role`. Compatible with the `where` function from Moose::Util::TypeConstraints, so don't worry about conflicts. Constants The following constants may be exported for convenience: `SCALAR` `ARRAY` `HASH` `CODE` `GLOB` `REF` `LVALUE` `IO` `VSTRING` `FORMAT` `REGEXP` `BOOLEAN` `STRING` `NUMBER` `SMARTMATCH` Export By default, only `does` is exported. This module uses Exporter::Tiny, so functions can be renamed: use Scalar::Does does => { -as => 'performs_role' }; Scalar::Does also plays some tricks with namespace::clean to ensure that any functions it exports to your namespace are cleaned up when you're finished with them. This ensures that if you're writing object-oriented code `does` and `overloads` will not be left hanging around as methods of your classes. Moose::Object provides a `does` method, and you should be able to use Scalar::Does without interfering with that. You can import the constants (plus `does`) using: use Scalar::Does -constants; The `make_role` and `where` functions can be exported like this: use Scalar::Does -make; Or list specific functions/constants that you wish to import: use Scalar::Does qw( does ARRAY HASH STRING NUMBER ); Custom Role Checks use Scalar::Does custom => { -as => 'does_array', -role => 'ARRAY' }, custom => { -as => 'does_hash', -role => 'HASH' }; does_array($thing); does_hash($thing); BUGS Please report any bugs to . SEE ALSO Scalar::Util. . Relationship to Moose roles Scalar::Does is not dependent on Moose, and its role-checking is not specific to Moose's idea of roles, but it does work well with Moose roles. Moose::Object overrides `DOES`, so Moose objects and Moose roles should "just work" with Scalar::Does. { package Transport; use Moose::Role; } { package Train; use Moose; with qw(Transport); } my $thomas = Train->new; does($thomas, 'Train'); # true does($thomas, 'Transport'); # true does($thomas, Transport->meta); # not yet supported! Mouse::Object should be compatible enough to work as well. See also: Moose::Role, Moose::Object, UNIVERSAL. Relationship to Moose type constraints Moose::Meta::TypeConstraint objects, plus the constants exported by MooseX::Types libraries all provide a `check` method, so again, should "just work" with Scalar::Does. Type constraint strings are not supported however. use Moose::Util::TypeConstraints qw(find_type_constraint); use MooseX::Types qw(Int); use Scalar::Does qw(does); my $int = find_type_constraint("Int"); does( "123", $int ); # true does( "123", Int ); # true does( "123", "Int" ); # false Mouse::Meta::TypeConstraints and MouseX::Types should be compatible enough to work as well. See also: Moose::Meta::TypeConstraint, Moose::Util::TypeConstraints, MooseX::Types, Scalar::Does::MooseTypes. Relationship to Type::Tiny type constraints Types built with Type::Tiny and Type::Library can be used exactly as Moose type constraint objects above. use Types::Standard qw(Int); use Scalar::Does qw(does); does(123, Int); # true In fact, Type::Tiny and related libraries are used extensively in the internals of Scalar::Does 0.200+. See also: Type::Tiny, Types::Standard. Relationship to Role::Tiny and Moo roles Roles using Role::Tiny 1.002000 and above provide a `DOES` method, so should work with Scalar::Does just like Moose roles. Prior to that release, Role::Tiny did not provide `DOES`. Moo's role system is based on Role::Tiny. See also: Role::Tiny, Moo::Role. AUTHOR Toby Inkster . COPYRIGHT AND LICENCE This software is copyright (c) 2012-2013 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.