Provided by: libspecio-perl_0.48-1_all 
NAME
Specio - Type constraints and coercions for Perl
VERSION
version 0.48
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>.
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>
• Vitaly Lipatov <lav@altlinux.ru>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2012 - 2022 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.