Dave Rolsky > Specio-0.06 > Specio

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Module Version: 0.06   Source   Latest Release: Specio-0.11

NAME ^

Specio - Type constraints and coercions for Perl

VERSION ^

version 0.06

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 ^

WARNING: This thing is very alpha.

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 it can be used 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 and 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 provides bool overloading.

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

The Num type accepts an object that provides 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, whenever possible, you're often better off making the parameter not required 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.

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:

LONG-TERM PLANS ^

Eventually I'd like to see this distro replace Moose's internal type system, which would also make MooseX::Types obsolete. This almost certainly means rewriting this distro to not use Moose itself (or any modules which use Moose, like Throwable).

For now, the current code is a proof of concept for the design.

BUGS ^

Please report any bugs or feature requests to bug-type@rt.cpan.org, or through the web interface at http://rt.cpan.org. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

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, which seems unlikely at best.

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

AUTHOR ^

Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE ^

This software is Copyright (c) 2013 by Dave Rolsky.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)
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