slightly better error handling

[gitmo/MooseX-Types.git] / lib / MooseX / Types.pm

package MooseX::Types;
use Moose;

=head1 NAME

MooseX::Types - Organise your Moose types in libraries

=cut

#use warnings;
#use strict;

use Moose::Util::TypeConstraints;
use MooseX::Types::TypeDecorator;
use MooseX::Types::Base             ();
use MooseX::Types::Util             qw( filter_tags );
use MooseX::Types::UndefinedType;
use Carp::Clan                      qw( ^MooseX::Types );

use namespace::clean -except => [qw( meta )];

our $VERSION = 0.06;

my $UndefMsg = q{Action for type '%s' not yet defined in library '%s'};

=head1 SYNOPSIS

=head2 Library Definition

  package MyLibrary;

  # predeclare our own types
  use MooseX::Types 
    -declare => [qw(
        PositiveInt NegativeInt
        ArrayRefOfPositiveInt ArrayRefOfAtLeastThreeNegativeInts
        LotsOfInnerConstraints StrOrArrayRef
    )];

  # import builtin types
  use MooseX::Types::Moose 'Int';

  # type definition
  subtype PositiveInt, 
      as Int, 
      where { $_ > 0 },
      message { "Int is not larger than 0" };
  
  subtype NegativeInt,
      as Int,
      where { $_ < 0 },
      message { "Int is not smaller than 0" };

  # type coercion
  coerce PositiveInt,
      from Int,
          via { 1 };

  # with parameterized constraints.
  
  subtype ArrayRefOfPositiveInt,
    as ArrayRef[PositiveInt];
    
  subtype ArrayRefOfAtLeastThreeNegativeInts,
    as ArrayRef[NegativeInt],
    where { scalar(@$_) > 2 };

  subtype LotsOfInnerConstraints,
    as ArrayRef[ArrayRef[HashRef[Int]]];
    
  # with TypeConstraint Unions
  
  subtype StrOrArrayRef,
    as Str|ArrayRef;

  1;

=head2 Usage

  package Foo;
  use Moose;
  use MyLibrary qw( PositiveInt NegativeInt );

  # use the exported constants as type names
  has 'bar',
      isa    => PositiveInt,
      is     => 'rw';
  has 'baz',
      isa    => NegativeInt,
      is     => 'rw';

  sub quux {
      my ($self, $value);

      # test the value
      print "positive\n" if is_PositiveInt($value);
      print "negative\n" if is_NegativeInt($value);

      # coerce the value, NegativeInt doesn't have a coercion
      # helper, since it didn't define any coercions.
      $value = to_PositiveInt($value) or die "Cannot coerce";
  }

  1;

=head1 DESCRIPTION

The types provided with L<Moose> are by design global. This package helps
you to organise and selectively import your own and the built-in types in
libraries. As a nice side effect, it catches typos at compile-time too.

However, the main reason for this module is to provide an easy way to not
have conflicts with your type names, since the internal fully qualified
names of the types will be prefixed with the library's name.

This module will also provide you with some helper functions to make it 
easier to use Moose types in your code.

=head1 TYPE HANDLER FUNCTIONS

=head2 $type

A constant with the name of your type. It contains the type's fully
qualified name. Takes no value, as all constants.

=head2 is_$type

This handler takes a value and tests if it is a valid value for this
C<$type>. It will return true or false.

=head2 to_$type

A handler that will take a value and coerce it into the C<$type>. It will
return a false value if the type could not be coerced.

B<Important Note>: This handler will only be exported for types that can
do type coercion. This has the advantage that a coercion to a type that
cannot hasn't defined any coercions will lead to a compile-time error.

=head1 LIBRARY DEFINITION

A MooseX::Types is just a normal Perl module. Unlike Moose 
itself, it does not install C<use strict> and C<use warnings> in your
class by default, so this is up to you.

The only thing a library is required to do is

  use MooseX::Types -declare => \@types;

with C<@types> being a list of types you wish to define in this library.
This line will install a proper base class in your package as well as the
full set of L<handlers|/"TYPE HANDLER FUNCTIONS"> for your declared 
types. It will then hand control over to L<Moose::Util::TypeConstraints>'
C<import> method to export the functions you will need to declare your
types.

If you want to use Moose' built-in types (e.g. for subtyping) you will 
want to 

  use MooseX::Types::Moose @types;

to import the helpers from the shipped L<MooseX::Types::Moose>
library which can export all types that come with Moose.

You will have to define coercions for your types or your library won't
export a L</to_$type> coercion helper for it.

Note that you currently cannot define types containing C<::>, since 
exporting would be a problem.

You also don't need to use C<warnings> and C<strict>, since the
definition of a library automatically exports those.

=head1 LIBRARY USAGE

You can import the L<"type helpers"|/"TYPE HANDLER FUNCTIONS"> of a
library by C<use>ing it with a list of types to import as arguments. If
you want all of them, use the C<:all> tag. For example:

  use MyLibrary      ':all';
  use MyOtherLibrary qw( TypeA TypeB );

MooseX::Types comes with a library of Moose' built-in types called
L<MooseX::Types::Moose>.

The exporting mechanism is, since version 0.5, implemented via a wrapper
around L<Sub::Exporter>. This means you can do something like this:

  use MyLibrary TypeA => { -as => 'MyTypeA' },
                TypeB => { -as => 'MyTypeB' };

=head1 WRAPPING A LIBRARY

You can define your own wrapper subclasses to manipulate the behaviour
of a set of library exports. Here is an example:

  package MyWrapper;
  use strict;
  use Class::C3;
  use base 'MooseX::Types::Wrapper';

  sub coercion_export_generator {
      my $class = shift;
      my $code = $class->next::method(@_);
      return sub {
          my $value = $code->(@_);
          warn "Coercion returned undef!"
              unless defined $value;
          return $value;
      };
  }

  1;

This class wraps the coercion generator (e.g., C<to_Int()>) and warns
if a coercion returned an undefined value. You can wrap any library
with this:

  package Foo;
  use strict;
  use MyWrapper MyLibrary => [qw( Foo Bar )],
                Moose     => [qw( Str Int )];

  ...
  1;

The C<Moose> library name is a special shortcut for 
L<MooseX::Types::Moose>.

=head2 Generator methods you can overload

=over 4

=item type_export_generator( $short, $full )

Creates a closure returning the type's L<Moose::Meta::TypeConstraint> 
object. 

=item check_export_generator( $short, $full, $undef_message )

This creates the closure used to test if a value is valid for this type.

=item coercion_export_generator( $short, $full, $undef_message )

This is the closure that's doing coercions.

=back

=head2 Provided Parameters

=over 4

=item $short

The short, exported name of the type.

=item $full

The fully qualified name of this type as L<Moose> knows it.

=item $undef_message

A message that will be thrown when type functionality is used but the
type does not yet exist.

=head1 NOTES REGARDING TYPE UNIONS

L<MooseX::Types> uses L<MooseX::Types::TypeDecorator> to do some overloading
which generally allows you to easily create union types:

  subtype StrOrArrayRef,
    as Str|ArrayRef;    

As with parameterized constrains, this overloading extends to modules using the
types you define in a type library.

    use Moose;
    use MooseX::Types::Moose qw(HashRef Int);
    
    has 'attr' => (isa=>HashRef|Int);

And everything should just work as you'd think.
    
=head1 METHODS

=head2 import

Installs the L<MooseX::Types::Base> class into the caller and 
exports types according to the specification described in 
L</"LIBRARY DEFINITION">. This will continue to 
L<Moose::Util::TypeConstraints>' C<import> method to export helper
functions you will need to declare your types.

=cut

sub import {
    my ($class, %args) = @_;
    my  $callee = caller;

    # everyone should want this
    strict->import;
    warnings->import;

    # inject base class into new library
    {   no strict 'refs';
        unshift @{ $callee . '::ISA' }, 'MooseX::Types::Base';
    }

    # generate predeclared type helpers
    if (my @orig_declare = @{ $args{ -declare } || [] }) {
        my ($tags, $declare) = filter_tags @orig_declare;
        my @to_export;

        for my $type (@$declare) {

            croak "Cannot create a type containing '::' ($type) at the moment"
                if $type =~ /::/;

            # add type to library and remember to export
            $callee->add_type($type);
            push @to_export, $type;
        }

        $callee->import({ -full => 1, -into => $callee }, @to_export);
    }

    # run type constraints import
    return Moose::Util::TypeConstraints->import({ into => $callee });
}

=head2 type_export_generator

Generate a type export, e.g. C<Int()>. This will return either a
L<Moose::Meta::TypeConstraint> object, or alternatively a
L<MooseX::Types::UndefinedType> object if the type was not
yet defined.

=cut

sub type_export_generator {
    my ($class, $type, $name) = @_;
    
    ## Return an anonymous subroutine that will generate the proxied type
    ## constraint for you.
    
    return sub {
        my $type_constraint;
        if(defined(my $params = shift @_)) {
            ## We currently only allow a TC to accept a single, ArrayRef
            ## parameter, as in HashRef[Int], where [Int] is what's inside the
            ## ArrayRef passed.
            if(ref $params eq 'ARRAY') {
                $type_constraint = $class->create_arged_type_constraint($name, @$params);
            } else {
                croak 'Arguments must be an ArrayRef, not '. ref $params;
            }
        } else {
            $type_constraint = $class->create_base_type_constraint($name);
        }
        $type_constraint = defined($type_constraint) ? $type_constraint
         : MooseX::Types::UndefinedType->new($name);
         
        my $type_decorator = $class->create_type_decorator($type_constraint);
        
        ## If there are additional args, that means it's probably stuff that
        ## needs to be returned to the subtype.  Not an ideal solution here but
        ## doesn't seem to cause trouble.
        
        if(@_) {
            return ($type_decorator, @_);
        } else {
            return $type_decorator;
        }
    };
}

=head2 create_arged_type_constraint ($name, @args)

Given a String $name with @args find the matching typeconstraint and parameterize
it with @args.

=cut

sub create_arged_type_constraint {
    my ($class, $name, @args) = @_;
    my $type_constraint = Moose::Util::TypeConstraints::find_or_create_type_constraint($name);
	return $type_constraint->parameterize(@args);
}

=head2 create_base_type_constraint ($name)

Given a String $name, find the matching typeconstraint.

=cut

sub create_base_type_constraint {
    my ($class, $name) = @_;
    return find_type_constraint($name);
}

=head2 create_type_decorator ($type_constraint)

Given a $type_constraint, return a lightweight L<MooseX::Types::TypeDecorator>
instance.

=cut

sub create_type_decorator {
    my ($class, $type_constraint) = @_;
    return MooseX::Types::TypeDecorator->new($type_constraint);
}

=head2 coercion_export_generator

This generates a coercion handler function, e.g. C<to_Int($value)>. 

=cut

sub coercion_export_generator {
    my ($class, $type, $full, $undef_msg) = @_;
    return sub {
        my ($value) = @_;

        # we need a type object
        my $tobj = find_type_constraint($full) or croak $undef_msg;
        my $return = $tobj->coerce($value);

        # non-successful coercion returns false
        return unless $tobj->check($return);

        return $return;
    }
}

=head2 check_export_generator

Generates a constraint check closure, e.g. C<is_Int($value)>.

=cut

sub check_export_generator {
    my ($class, $type, $full, $undef_msg) = @_;
    return sub {
        my ($value) = @_;

        # we need a type object
        my $tobj = find_type_constraint($full) or croak $undef_msg;

        return $tobj->check($value);
    }
}

=head1 CAVEATS

The following are lists of gotcha's and their workarounds for developers coming
from the standard string based type constraint names

=head2 Uniqueness

A library makes the types quasi-unique by prefixing their names with (by
default) the library package name. If you're only using the type handler
functions provided by MooseX::Types, you shouldn't ever have to use
a type's actual full name.

=head2 Argument separation ('=>' versus ',')

The Perlop manpage has this to say about the '=>' operator: "The => operator is
a synonym for the comma, but forces any word (consisting entirely of word
characters) to its left to be interpreted as a string (as of 5.001). This
includes words that might otherwise be considered a constant or function call."

Due to this stringification, the following will NOT work as you might think:

  subtype StrOrArrayRef => as Str|ArrayRef;
  
The 'StrOrArrayRef' will have it's stringification activated this causes the
subtype to not be created.  Since the bareword type constraints are not strings
you really should not try to treat them that way.  You will have to use the ','
operator instead.  The author's of this package realize that all the L<Moose>
documention and examples nearly uniformly use the '=>' version of the comma
operator and this could be an issue if you are converting code.

Patches welcome for discussion.
    
=head1 SEE ALSO

L<Moose>, 
L<Moose::Util::TypeConstraints>, 
L<MooseX::Types::Moose>,
L<Sub::Exporter>

=head1 AUTHOR AND COPYRIGHT

Robert 'phaylon' Sedlacek C<E<lt>rs@474.atE<gt>>, with many thanks to
the C<#moose> cabal on C<irc.perl.org>.

Additional features by John Napiorkowski (jnapiorkowski) <jjnapiork@cpan.org>.

=head1 LICENSE

This program is free software; you can redistribute it and/or modify
it under the same terms as perl itself.

=cut

1;