Provided by: libspecio-perl_0.44-1_all bug

NAME

       Specio - Type constraints and coercions for Perl

VERSION

       version 0.44

SYNOPSIS

           package MyApp::Type::Library;

           use Specio::Declare;
           use Specio::Library::Builtins;

           declare(
               'PositiveInt',
               parent => t('Int'),
               inline => sub {
                   $_[0]->parent->inline_check( $_[1] )
                       . ' && ( '
                       . $_[1]
                       . ' > 0 )';
               },
           );

           # or ...

           declare(
               'PositiveInt',
               parent => t('Int'),
               where  => sub { $_[0] > 0 },
           );

           declare(
               'ArrayRefOfPositiveInt',
               parent => t(
                   'ArrayRef',
                   of => t('PositiveInt'),
               ),
           );

           coerce(
               'ArrayRefOfPositiveInt',
               from  => t('PositiveInt'),
               using => sub { [ $_[0] ] },
           );

           any_can_type(
               'Duck',
               methods => [ 'duck_walk', 'quack' ],
           );

           object_isa_type('MyApp::Person');

DESCRIPTION

       The "Specio" distribution provides classes for representing type constraints and coercion,
       along with syntax sugar for declaring them.

       Note that this is not a proper type system for Perl. Nothing in this distribution will
       magically make the Perl interpreter start checking a value's type on assignment to a
       variable. In fact, there's no built-in way to apply a type to a variable at all.

       Instead, you can explicitly check a value against a type, and optionally coerce values to
       that type.

       My long-term goal is to replace Moose's built-in types and MooseX::Types with this module.

WHAT IS A TYPE?

       At it's core, a type is simply a constraint. A constraint is code that checks a value and
       returns true or false. Most constraints are represented by Specio::Constraint::Simple
       objects. However, there are other type constraint classes for specialized kinds of
       constraints.

       Types can be named or anonymous, and each type can have a parent type. A type's constraint
       is optional because sometimes you may want to create a named subtype of some existing type
       without adding additional constraints.

       Constraints can be expressed either in terms of a simple subroutine reference or in terms
       of an inline generator subroutine reference. The former is easier to write but the latter
       is preferred because it allow for better optimization.

       A type can also have an optional message generator subroutine reference. You can use this
       to provide a more intelligent error message when a value does not pass the constraint,
       though the default message should suffice for most cases.

       Finally, you can associate a set of coercions with a type. A coercion is a subroutine
       reference (or inline generator, like constraints), that takes a value of one type and
       turns it into a value that matches the type the coercion belongs to.

BUILTIN TYPES

       This distribution ships with a set of builtin types representing the types provided by the
       Perl interpreter itself. They are arranged in a hierarchy as follows:

         Item
             Bool
             Maybe (of `a)
             Undef
             Defined
                 Value
                     Str
                         Num
                             Int
                         ClassName
                 Ref
                     ScalarRef (of `a)
                     ArrayRef (of `a)
                     HashRef (of `a)
                     CodeRef
                     RegexpRef
                     GlobRef
                     FileHandle
                     Object

       The "Item" type accepts anything and everything.

       The "Bool" type only accepts "undef", 0, or 1.

       The "Undef" type only accepts "undef".

       The "Defined" type accepts anything except "undef".

       The "Num" and "Int" types are stricter about numbers than Perl is. Specifically, they do
       not allow any sort of space in the number, nor do they accept "Nan", "Inf", or "Infinity".

       The "ClassName" type constraint checks that the name is valid and that the class is
       loaded.

       The "FileHandle" type accepts either a glob, a scalar filehandle, or anything that isa
       IO::Handle.

       All types accept overloaded objects that support the required operation. See below for
       details.

   Overloading
       Perl's overloading is horribly broken and doesn't make much sense at all.

       However, unlike Moose, all type constraints allow overloaded objects where they make
       sense.

       For types where overloading makes sense, we explicitly check that the object provides the
       type overloading we expect. We do not simply try to use the object as the type in question
       and hope it works. This means that these checks effectively ignore the "fallback" setting
       for the overloaded object. In other words, an object that overloads stringification will
       not pass the "Bool" type check unless it also overloads boolification.

       Most types do not check that the overloaded method actually returns something that matches
       the constraint. This may change in the future.

       The "Bool" type accepts an object that implements "bool" overloading.

       The "Str" type accepts an object that implements string ("q{""}") overloading.

       The "Num" type accepts an object that implements numeric ("'0+'}") overloading. The "Int"
       type does as well, but it will check that the overloading returns an actual integer.

       The "ClassName" type will accept an object with string overloading that returns a class
       name.

       To make this all more confusing, the "Value" type will never accept an object, even though
       some of its subtypes will.

       The various reference types all accept objects which provide the appropriate overloading.
       The "FileHandle" type accepts an object which overloads globification as long as the
       returned glob is an open filehandle.

PARAMETERIZABLE TYPES

       Any type followed by a type parameter "of `a" in the hierarchy above can be parameterized.
       The parameter is itself a type, so you can say you want an "ArrayRef of Int", or even an
       "ArrayRef of HashRef of ScalarRef of ClassName".

       When they are parameterized, the "ScalarRef" and "ArrayRef" types check that the value(s)
       they refer to match the type parameter. For the "HashRef" type, the parameter applies to
       the values (keys are never checked).

   Maybe
       The "Maybe" type is a special parameterized type. It allows for either "undef" or a value.
       All by itself, it is meaningless, since it is equivalent to "Maybe of Item", which is
       equivalent to Item. When parameterized, it accepts either an "undef" or the type of its
       parameter.

       This is useful for optional attributes or parameters. However, you're probably better off
       making your code simply not pass the parameter at all This usually makes for a simpler
       API.

REGISTRIES AND IMPORTING

       Types are local to each package where they are used. When you "import" types from some
       other library, you are actually making a copy of that type.

       This means that a type named "Foo" in one package may not be the same as "Foo" in another
       package. This has potential for confusion, but it also avoids the magic action at a
       distance pollution that comes with a global type naming system.

       The registry is managed internally by the Specio distribution's modules, and is not
       exposed to your code. To access a type, you always call "t('TypeName')".

       This returns the named type or dies if no such type exists.

       Because types are always copied on import, it's safe to create coercions on any type. Your
       coercion from "Str" to "Int" will not be seen by any other package, unless that package
       explicitly imports your "Int" type.

       When you import types, you import every type defined in the package you import from.
       However, you can overwrite an imported type with your own type definition. You cannot
       define the same type twice internally.

CREATING A TYPE LIBRARY

       By default, all types created inside a package are invisible to other packages. If you
       want to create a type library, you need to inherit from Specio::Exporter package:

         package MyApp::Type::Library;

         use parent 'Specio::Exporter';

         use Specio::Declare;
         use Specio::Library::Builtins;

         declare(
             'Foo',
             parent => t('Str'),
             where  => sub { $_[0] =~ /foo/i },
         );

       Now the MyApp::Type::Library package will export a single type named "Foo". It does not
       re-export the types provided by Specio::Library::Builtins.

       If you want to make your library re-export some other libraries types, you can ask for
       this explicitly:

         package MyApp::Type::Library;

         use parent 'Specio::Exporter';

         use Specio::Declare;
         use Specio::Library::Builtins -reexport;

         declare( 'Foo, ... );

       Now MyApp::Types::Library exports any types it defines, as well as all the types defined
       in Specio::Library::Builtins.

DECLARING TYPES

       Use the Specio::Declare module to declare types. It exports a set of helpers for declaring
       types. See that module's documentation for more details on these helpers.

USING SPECIO WITH Moose

       This should just work. Use a Specio type anywhere you'd specify a type.

USING SPECIO WITH Moo

       Using Specio with Moo is easy. You can pass Specio constraint objects as "isa" parameters
       for attributes. For coercions, simply call "$type->coercion_sub".

           package Foo;

           use Specio::Declare;
           use Specio::Library::Builtins;
           use Moo;

           my $str_type = t('Str');
           has string => (
              is  => 'ro',
              isa => $str_type,
           );

           my $ucstr = declare(
               'UCStr',
               parent => t('Str'),
               where  => sub { $_[0] =~ /^[A-Z]+$/ },
           );

           coerce(
               $ucstr,
               from  => t('Str'),
               using => sub { return uc $_[0] },
           );

           has ucstr => (
               is     => 'ro',
               isa    => $ucstr,
               coerce => $ucstr->coercion_sub,
           );

       The subs returned by Specio use Sub::Quote internally and are suitable for inlining.

USING SPECIO WITH OTHER THINGS

       See Specio::Constraint::Simple for the API that all constraint objects share.

Moose, MooseX::Types, and Specio

       This module aims to supplant both Moose's built-in type system (see
       Moose::Util::TypeConstraints aka MUTC) and MooseX::Types, which attempts to patch some of
       the holes in the Moose built-in type design.

       Here are some of the salient differences:

       ·   Types names are strings, but they're not global

           Unlike Moose and MooseX::Types, type names are always local to the current package.
           There is no possibility of name collision between different modules, so you can safely
           use short type names.

           Unlike MooseX::Types, types are strings, so there is no possibility of colliding with
           existing class or subroutine names.

       ·   No type auto-creation

           Types are always retrieved using the "t()" subroutine. If you pass an unknown name to
           this subroutine it dies. This is different from Moose and MooseX::Types, which assume
           that unknown names are class names.

       ·   Anon types are explicit

           With Moose and MooseX::Types, you use the same subroutine, "subtype()", to declare
           both named and anonymous types. With Specio, you use "declare()" for named types and
           "anon()" for anonymous types.

       ·   Class and object types are separate

           Moose and MooseX::Types have "class_type" and "duck_type". The former type requires an
           object, while the latter accepts a class name or object.

           With Specio, the distinction between accepting an object versus object or class is
           explicit. There are six declaration helpers, "object_can_type", "object_does_type",
           "object_isa_type", "any_can_type", "any_does_type", and "any_isa_type".

       ·   Overloading support is baked in

           Perl's overloading is quite broken but ignoring it makes Moose's type system
           frustrating to use in many cases.

       ·   Types can either have a constraint or inline generator, not both

           Moose and MooseX::Types types can be defined with a subroutine reference as the
           constraint, an inline generator subroutine, or both. This is purely for backwards
           compatibility, and it makes the internals more complicated than they need to be.

           With Specio, a constraint can have either a subroutine reference or an inline
           generator, not both.

       ·   Coercions can be inlined

           I simply never got around to implementing this in Moose.

       ·   No crazy coercion features

           Moose has some bizarre (and mostly) undocumented features relating to coercions and
           parameterizable types. This is a misfeature.

OPTIONAL PREREQS

       There are several optional prereqs that if installed will make this distribution better in
       some way.

       ·   Ref::Util

           Installing this will speed up a number of type checks for built-in types.

       ·   XString

           If this is installed it will be loaded instead of the B module if you have Perl 5.10
           or greater. This module is much more memory efficient than loading all of B.

       ·   Sub::Util or Sub::Name

           If one of these is installed then stack traces that end up in Specio code will have
           much better subroutine names for any frames.

WHY THE NAME?

       This distro was originally called "Type", but that's an awfully generic top level
       namespace. Specio is Latin for for "look at" and "spec" is the root for the word
       "species". It's short, relatively easy to type, and not used by any other distro.

LONG-TERM PLANS

       Eventually I'd like to see this distro replace Moose's internal type system, which would
       also make MooseX::Types obsolete.

SUPPORT

       Bugs may be submitted at <https://github.com/houseabsolute/Specio/issues>.

       I am also usually active on IRC as 'autarch' on "irc://irc.perl.org".

SOURCE

       The source code repository for Specio can be found at
       <https://github.com/houseabsolute/Specio>.

DONATIONS

       If you'd like to thank me for the work I've done on this module, please consider making a
       "donation" to me via PayPal. I spend a lot of free time creating free software, and would
       appreciate any support you'd care to offer.

       Please note that I am not suggesting that you must do this in order for me to continue
       working on this particular software. I will continue to do so, inasmuch as I have in the
       past, for as long as it interests me.

       Similarly, a donation made in this way will probably not make me work on this software
       much more, unless I get so many donations that I can consider working on free software
       full time (let's all have a chuckle at that together).

       To donate, log into PayPal and send money to autarch@urth.org, or use the button at
       <http://www.urth.org/~autarch/fs-donation.html>.

AUTHOR

       Dave Rolsky <autarch@urth.org>

CONTRIBUTORS

       ·   Chris White <chrisw@leehayes.com>

       ·   cpansprout <cpansprout@gmail.com>

       ·   Graham Knop <haarg@haarg.org>

       ·   Karen Etheridge <ether@cpan.org>

COPYRIGHT AND LICENSE

       This software is Copyright (c) 2012 - 2019 by Dave Rolsky.

       This is free software, licensed under:

         The Artistic License 2.0 (GPL Compatible)

       The full text of the license can be found in the LICENSE file included with this
       distribution.