Effort to the strict constructor

[gitmo/Mouse.git] / lib / Mouse / Meta / Attribute.pm

package Mouse::Meta::Attribute;
use Mouse::Util qw(:meta); # enables strict and warnings

use Carp ();

use Mouse::Meta::TypeConstraint;

#my @attributes = qw(
#    name init_arg required
#    is
#    isa does coerce
#    accessor reader writer predicate clearer
#    default builder lazy lazy_build
#    auto_deref trigger
#    metaclass traits
#
#    handles
#    documentation
#
#    type_constraint
#);

sub _process_options{
    my($class, $name, $args) = @_;

    # taken from Class::MOP::Attribute::new

    defined($name)
        or $class->throw_error('You must provide a name for the attribute');

    if(!exists $args->{init_arg}){
        $args->{init_arg} = $name;
    }

    # 'required' requires eigher 'init_arg', 'builder', or 'default'
    my $can_be_required = defined( $args->{init_arg} );

    if(exists $args->{builder}){
        # XXX:
        # Moose refuses a CODE ref builder, but Mouse doesn't for backward compatibility
        # This feature will be changed in a future. (gfx)
        $class->throw_error('builder must be a defined scalar value which is a method name')
            #if ref $args->{builder} || !defined $args->{builder};
            if !defined $args->{builder};

        $can_be_required++;
    }
    elsif(exists $args->{default}){
        if(ref $args->{default} && ref($args->{default}) ne 'CODE'){
            $class->throw_error("References are not allowed as default values, you must "
                              . "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])");
        }
        $can_be_required++;
    }

    if( $args->{required} && !$can_be_required ) {
        $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg");
    }

    # taken from Mouse::Meta::Attribute->new and _process_args->

    if(exists $args->{is}){
        my $is = $args->{is};

        if($is eq 'ro'){
            $args->{reader} ||= $name;
        }
        elsif($is eq 'rw'){
            if(exists $args->{writer}){
                $args->{reader} ||= $name;
             }
             else{
                $args->{accessor} ||= $name;
             }
        }
        elsif($is eq 'bare'){
            # do nothing, but don't complain (later) about missing methods
        }
        else{
            $is = 'undef' if !defined $is;
            $class->throw_error("I do not understand this option (is => $is) on attribute ($name)");
        }
    }

    my $tc;
    if(exists $args->{isa}){
        $args->{type_constraint} = Mouse::Util::TypeConstraints::find_or_create_isa_type_constraint($args->{isa});
    }
    elsif(exists $args->{does}){
        $args->{type_constraint} = Mouse::Util::TypeConstraints::find_or_create_does_type_constraint($args->{does});
    }
    $tc = $args->{type_constraint};

    if($args->{coerce}){
        defined($tc)
            || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)");

        $args->{weak_ref}
            && $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)");
    }

    if ($args->{lazy_build}) {
        exists($args->{default})
            && $class->throw_error("You can not use lazy_build and default for the same attribute ($name)");

        $args->{lazy}      = 1;
        $args->{builder} ||= "_build_${name}";
        if ($name =~ /^_/) {
            $args->{clearer}   ||= "_clear${name}";
            $args->{predicate} ||= "_has${name}";
        }
        else {
            $args->{clearer}   ||= "clear_${name}";
            $args->{predicate} ||= "has_${name}";
        }
    }

    if ($args->{auto_deref}) {
        defined($tc)
            || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)");

        ( $tc->is_a_type_of('ArrayRef') || $tc->is_a_type_of('HashRef') )
            || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)");
    }

    if (exists $args->{trigger}) {
        ('CODE' eq ref $args->{trigger})
            || $class->throw_error("Trigger must be a CODE ref on attribute ($name)");
    }

    if ($args->{lazy}) {
        (exists $args->{default} || defined $args->{builder})
            || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it");
    }

    return;
}

sub new {
    my $class = shift;
    my $name  = shift;

    my %args  = (@_ == 1) ? %{ $_[0] } : @_;

    $class->_process_options($name, \%args);

    $args{name} = $name;

    my $self = bless \%args, $class;

    # extra attributes
    if($class ne __PACKAGE__){
        $class->meta->_initialize_object($self, \%args);
    }

# XXX: there is no fast way to check attribute validity
#    my @bad = ...;
#    if(@bad){
#        @bad = sort @bad;
#        Carp::cluck("Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad");
#    }

    return $self;
}

sub has_read_method      { $_[0]->has_reader || $_[0]->has_accessor }
sub has_write_method     { $_[0]->has_writer || $_[0]->has_accessor }

sub interpolate_class{
    my($class, $args) = @_;

    if(my $metaclass = delete $args->{metaclass}){
        $class = Mouse::Util::resolve_metaclass_alias( Attribute => $metaclass );
    }

    my @traits;
    if(my $traits_ref = delete $args->{traits}){

        for (my $i = 0; $i < @{$traits_ref}; $i++) {
            my $trait = Mouse::Util::resolve_metaclass_alias(Attribute => $traits_ref->[$i], trait => 1);

            next if $class->does($trait);

            push @traits, $trait;

            # are there options?
            push @traits, $traits_ref->[++$i]
                if ref($traits_ref->[$i+1]);
        }

        if (@traits) {
            $class = Mouse::Meta::Class->create_anon_class(
                superclasses => [ $class ],
                roles        => \@traits,
                cache        => 1,
            )->name;
        }
    }

    return( $class, @traits );
}

sub _coerce_and_verify {
    my($self, $value, $instance) = @_;

    my $type_constraint = $self->{type_constraint};
    return $value if !defined $type_constraint;

    if ($self->should_coerce && $type_constraint->has_coercion) {
        $value = $type_constraint->coerce($value);
    }

    $self->verify_against_type_constraint($value);

    return $value;
}

sub verify_against_type_constraint {
    my ($self, $value) = @_;

    my $type_constraint = $self->{type_constraint};
    return 1 if !$type_constraint;
    return 1 if $type_constraint->check($value);

    $self->_throw_type_constraint_error($value, $type_constraint);
}

sub _throw_type_constraint_error {
    my($self, $value, $type) = @_;

    $self->throw_error(
        sprintf q{Attribute (%s) does not pass the type constraint because: %s},
            $self->name,
            $type->get_message($value),
    );
}

sub clone_and_inherit_options{
    my($self, %args) = @_;

    my($attribute_class, @traits) = ref($self)->interpolate_class(\%args);

    $args{traits} = \@traits if @traits;
    # do not inherit the 'handles' attribute
    foreach my $name(keys %{$self}){
        if(!exists $args{$name} && $name ne 'handles'){
            $args{$name} = $self->{$name};
        }
    }
    return $attribute_class->new($self->name, %args);
}

sub get_read_method {
    return $_[0]->reader || $_[0]->accessor
}
sub get_write_method {
    return $_[0]->writer || $_[0]->accessor
}

sub _get_accessor_method_ref {
    my($self, $type, $generator) = @_;

    my $metaclass = $self->associated_class
        || $self->throw_error('No asocciated class for ' . $self->name);

    my $accessor = $self->$type();
    if($accessor){
        return $metaclass->get_method_body($accessor);
    }
    else{
        return $self->accessor_metaclass->$generator($self, $metaclass);
    }
}

sub get_read_method_ref{
    my($self) = @_;
    return $self->{_read_method_ref} ||= $self->_get_accessor_method_ref('get_read_method', '_generate_reader');
}

sub get_write_method_ref{
    my($self) = @_;
    return $self->{_write_method_ref} ||= $self->_get_accessor_method_ref('get_write_method', '_generate_writer');
}

sub set_value {
    my($self, $object, $value) = @_;
    return $self->get_write_method_ref()->($object, $value);
}

sub get_value {
    my($self, $object) = @_;
    return $self->get_read_method_ref()->($object);
}

sub has_value {
    my($self, $object) = @_;
    my $accessor_ref = $self->{_predicate_ref}
        ||= $self->_get_accessor_method_ref('predicate', '_generate_predicate');

    return $accessor_ref->($object);
}

sub clear_value {
    my($self, $object) = @_;
    my $accessor_ref = $self->{_crealer_ref}
        ||= $self->_get_accessor_method_ref('clearer', '_generate_clearer');

    return $accessor_ref->($object);
}


sub associate_method{
    my ($attribute, $method_name) = @_;
    $attribute->{associated_methods}++;
    return;
}

sub install_accessors{
    my($attribute) = @_;

    my $metaclass      = $attribute->associated_class;
    my $accessor_class = $attribute->accessor_metaclass;

    foreach my $type(qw(accessor reader writer predicate clearer)){
        if(exists $attribute->{$type}){
            my $generator = '_generate_' . $type;
            my $code      = $accessor_class->$generator($attribute, $metaclass);
            $metaclass->add_method($attribute->{$type} => $code);
            $attribute->associate_method($attribute->{$type});
        }
    }

    # install delegation
    if(exists $attribute->{handles}){
        my %handles = $attribute->_canonicalize_handles($attribute->{handles});

        while(my($handle, $method_to_call) = each %handles){
            $metaclass->add_method($handle =>
                $attribute->_make_delegation_method(
                    $handle, $method_to_call));

            $attribute->associate_method($handle);
        }
    }

    return;
}

sub delegation_metaclass() { 'Mouse::Meta::Method::Delegation' }

sub _canonicalize_handles {
    my($self, $handles) = @_;

    if (ref($handles) eq 'HASH') {
        return %$handles;
    }
    elsif (ref($handles) eq 'ARRAY') {
        return map { $_ => $_ } @$handles;
    }
    elsif (ref($handles) eq 'Regexp') {
        my $class_or_role = ($self->{isa} || $self->{does})
            || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)");

        my $meta = Mouse::Meta::Class->initialize("$class_or_role"); # "" for stringify
        return map  { $_ => $_ }
               grep { !Mouse::Object->can($_) && $_ =~ $handles }
                   Mouse::Util::is_a_metarole($meta)
                        ? $meta->get_method_list
                        : $meta->get_all_method_names;
    }
    else {
        $self->throw_error("Unable to canonicalize the 'handles' option with $handles");
    }
}

sub _make_delegation_method {
    my($self, $handle, $method_to_call) = @_;
    my $delegator = $self->delegation_metaclass;
    Mouse::Util::load_class($delegator);

    return $delegator->_generate_delegation($self, $handle, $method_to_call);
}

sub throw_error{
    my $self = shift;

    my $metaclass = (ref $self && $self->associated_class) || 'Mouse::Meta::Class';
    $metaclass->throw_error(@_, depth => 1);
}

1;
__END__

=head1 NAME

Mouse::Meta::Attribute - The Mouse attribute metaclass

=head1 VERSION

This document describes Mouse version 0.45

=head1 METHODS

=head2 C<< new(%options) -> Mouse::Meta::Attribute >>

Instantiates a new Mouse::Meta::Attribute. Does nothing else.

It adds the following options to the constructor:

=over 4

=item C<< is => 'ro', 'rw', 'bare' >>

This provides a shorthand for specifying the C<reader>, C<writer>, or
C<accessor> names. If the attribute is read-only ('ro') then it will
have a C<reader> method with the same attribute as the name.

If it is read-write ('rw') then it will have an C<accessor> method
with the same name. If you provide an explicit C<writer> for a
read-write attribute, then you will have a C<reader> with the same
name as the attribute, and a C<writer> with the name you provided.

Use 'bare' when you are deliberately not installing any methods
(accessor, reader, etc.) associated with this attribute; otherwise,
Moose will issue a deprecation warning when this attribute is added to a
metaclass.

=item C<< isa => Type >>

This option accepts a type. The type can be a string, which should be
a type name. If the type name is unknown, it is assumed to be a class
name.

This option can also accept a L<Moose::Meta::TypeConstraint> object.

If you I<also> provide a C<does> option, then your C<isa> option must
be a class name, and that class must do the role specified with
C<does>.

=item C<< does => Role >>

This is short-hand for saying that the attribute's type must be an
object which does the named role.

B<This option is not yet supported.>

=item C<< coerce => Bool >>

This option is only valid for objects with a type constraint
(C<isa>). If this is true, then coercions will be applied whenever
this attribute is set.

You can make both this and the C<weak_ref> option true.

=item C<< trigger => CodeRef >>

This option accepts a subroutine reference, which will be called after
the attribute is set.

=item C<< required => Bool >>

An attribute which is required must be provided to the constructor. An
attribute which is required can also have a C<default> or C<builder>,
which will satisfy its required-ness.

A required attribute must have a C<default>, C<builder> or a
non-C<undef> C<init_arg>

=item C<< lazy => Bool >>

A lazy attribute must have a C<default> or C<builder>. When an
attribute is lazy, the default value will not be calculated until the
attribute is read.

=item C<< weak_ref => Bool >>

If this is true, the attribute's value will be stored as a weak
reference.

=item C<< auto_deref => Bool >>

If this is true, then the reader will dereference the value when it is
called. The attribute must have a type constraint which defines the
attribute as an array or hash reference.

=item C<< lazy_build => Bool >>

Setting this to true makes the attribute lazy and provides a number of
default methods.

  has 'size' => (
      is         => 'ro',
      lazy_build => 1,
  );

is equivalent to this:

  has 'size' => (
      is        => 'ro',
      lazy      => 1,
      builder   => '_build_size',
      clearer   => 'clear_size',
      predicate => 'has_size',
  );

=back

=head2 C<< associate_method(MethodName) >>

Associates a method with the attribute. Typically, this is called internally
when an attribute generates its accessors.

Currently the argument I<MethodName> is ignored in Mouse.

=head2 C<< verify_against_type_constraint(Item) -> TRUE | ERROR >>

Checks that the given value passes this attribute's type constraint. Returns C<true>
on success, otherwise C<confess>es.

=head2 C<< clone_and_inherit_options(options) -> Mouse::Meta::Attribute >>

Creates a new attribute in the owner class, inheriting options from parent classes.
Accessors and helper methods are installed. Some error checking is done.

=head2 C<< get_read_method_ref >>

=head2 C<< get_write_method_ref >>

Returns the subroutine reference of a method suitable for reading or
writing the attribute's value in the associated class. These methods
always return a subroutine reference, regardless of whether or not the
attribute is read- or write-only.

=head1 SEE ALSO

L<Moose::Meta::Attribute>

L<Class::MOP::Attribute>

=cut