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29 Jan 2021 19:06:54 UTC
- Distribution: Specio
- Module version: 0.47
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- License: artistic_2
- Perl: v5.8.0
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- NAME
- VERSION
- SYNOPSIS
- DESCRIPTION
- WHAT IS A TYPE?
- BUILTIN TYPES
- PARAMETERIZABLE TYPES
- REGISTRIES AND IMPORTING
- CREATING A TYPE LIBRARY
- DECLARING TYPES
- USING SPECIO WITH Moose
- USING SPECIO WITH Moo
- USING SPECIO WITH OTHER THINGS
- Moose, MooseX::Types, and Specio
- OPTIONAL PREREQS
- WHY THE NAME?
- LONG-TERM PLANS
- SUPPORT
- SOURCE
- DONATIONS
- AUTHOR
- CONTRIBUTORS
- COPYRIGHT AND LICENSE
NAME
Specio - Type constraints and coercions for Perl
VERSION
version 0.47
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 acceptsundef
,0
, or1
.The
Undef
type only acceptsundef
.The
Defined
type accepts anything exceptundef
.The
Num
andInt
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 theBool
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 implementsbool
overloading.The
Str
type accepts an object that implements string (q{""}
) overloading.The
Num
type accepts an object that implements numeric ('0+'}
) overloading. TheInt
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
andArrayRef
types check that the value(s) they refer to match the type parameter. For theHashRef
type, the parameter applies to the values (keys are never checked).Maybe
The
Maybe
type is a special parameterized type. It allows for eitherundef
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 anundef
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
toInt
will not be seen by any other package, unless that package explicitly imports yourInt
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 usedeclare()
for named types andanon()
for anonymous types.Class and object types are separate
Moose and MooseX::Types have
class_type
andduck_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
, andany_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.
-
Installing this will speed up a number of type checks for built-in types.
-
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.
-
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 https://www.urth.org/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 - 2021 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.
Module Install Instructions
To install Specio, copy and paste the appropriate command in to your terminal.
cpanm Specio
perl -MCPAN -e shell install Specio
For more information on module installation, please visit the detailed CPAN module installation guide.