my ($attr_name, $type, $accessor) = @_;
my %ACCESSOR_TEMPLATES = (
- 'accessor' => sub {
- $_[0]->{$attr_name} = $_[1] if scalar(@_) == 2;
- $_[0]->{$attr_name};
- },
- 'reader' => sub {
- $_[0]->{$attr_name};
- },
- 'writer' => sub {
- $_[0]->{$attr_name} = $_[1];
- return;
- },
- 'predicate' => sub {
- return defined $_[0]->{$attr_name} ? 1 : 0;
- }
+ 'accessor' => qq{sub {
+ \$_[0]->{'$attr_name'} = \$_[1] if scalar(\@_) == 2;
+ \$_[0]->{'$attr_name'};
+ }},
+ 'reader' => qq{sub {
+ \$_[0]->{'$attr_name'};
+ }},
+ 'writer' => qq{sub {
+ \$_[0]->{'$attr_name'} = \$_[1];
+ }},
+ 'predicate' => qq{sub {
+ defined \$_[0]->{'$attr_name'} ? 1 : 0;
+ }}
);
if (reftype($accessor) && reftype($accessor) eq 'HASH') {
return ($name, Class::MOP::Attribute::Accessor->wrap($method));
}
else {
- return ($accessor => Class::MOP::Attribute::Accessor->wrap($ACCESSOR_TEMPLATES{$type}));
+ my $method = eval $ACCESSOR_TEMPLATES{$type};
+ confess "Could not create the $type for $attr_name CODE(\n" . $ACCESSOR_TEMPLATES{$type} . "\n) : $@" if $@;
+ return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
}
};
my ($self, $class) = @_;
(blessed($class) && $class->isa('Class::MOP::Class'))
|| confess "You must pass a Class::MOP::Class instance (or a subclass)";
-
$class->add_method(
$_inspect_accessor->($self->name, 'accessor' => $self->accessor())
) if $self->has_accessor();
$class->add_method(
$_inspect_accessor->($self->name, 'predicate' => $self->predicate())
) if $self->has_predicate();
+ return;
}
}
-sub remove_accessors {
- my ($self, $class) = @_;
- (blessed($class) && $class->isa('Class::MOP::Class'))
- || confess "You must pass a Class::MOP::Class instance (or a subclass)";
-
- if ($self->has_accessor()) {
- my $accessor = $self->accessor();
+{
+ my $_remove_accessor = sub {
+ my ($accessor, $class) = @_;
if (reftype($accessor) && reftype($accessor) eq 'HASH') {
($accessor) = keys %{$accessor};
}
- my $method = $class->get_method($accessor);
- $class->remove_method($accessor)
+ my $method = $class->get_method($accessor);
+ $class->remove_method($accessor)
if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
- }
- else {
- if ($self->has_reader()) {
- my $reader = $self->reader();
- if (reftype($reader) && reftype($reader) eq 'HASH') {
- ($reader) = keys %{$reader};
- }
- my $method = $class->get_method($reader);
- $class->remove_method($reader)
- if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
- }
- if ($self->has_writer()) {
- my $writer = $self->writer();
- if (reftype($writer) && reftype($writer) eq 'HASH') {
- ($writer) = keys %{$writer};
- }
- my $method = $class->get_method($writer);
- $class->remove_method($writer)
- if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
- }
- }
+ };
- if ($self->has_predicate()) {
- my $predicate = $self->predicate();
- if (reftype($predicate) && reftype($predicate) eq 'HASH') {
- ($predicate) = keys %{$predicate};
- }
- my $method = $class->get_method($predicate);
- $class->remove_method($predicate)
- if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
- }
+ sub remove_accessors {
+ my ($self, $class) = @_;
+ (blessed($class) && $class->isa('Class::MOP::Class'))
+ || confess "You must pass a Class::MOP::Class instance (or a subclass)";
+ $_remove_accessor->($self->accessor(), $class) if $self->has_accessor();
+ $_remove_accessor->($self->reader(), $class) if $self->has_reader();
+ $_remove_accessor->($self->writer(), $class) if $self->has_writer();
+ $_remove_accessor->($self->predicate(), $class) if $self->has_predicate();
+ return;
+ }
+
}
package Class::MOP::Attribute::Accessor;
=head1 SYNOPSIS
Class::MOP::Attribute->new('$foo' => (
- accessor => 'foo', # dual purpose get/set accessor
- init_arg => '-foo', # class->new will look for a -foo key
- default => 'BAR IS BAZ!' # if no -foo key is provided, use this
+ accessor => 'foo', # dual purpose get/set accessor
+ predicate => 'has_foo' # predicate check for defined-ness
+ init_arg => '-foo', # class->new will look for a -foo key
+ default => 'BAR IS BAZ!' # if no -foo key is provided, use this
));
Class::MOP::Attribute->new('$.bar' => (
- reader => 'bar', # getter
- writer => 'set_bar', # setter
- init_arg => '-bar', # class->new will look for a -bar key
+ reader => 'bar', # getter
+ writer => 'set_bar', # setter
+ predicate => 'has_bar' # predicate check for defined-ness
+ init_arg => ':bar', # class->new will look for a :bar key
# no default value means it is undef
));
=head1 DESCRIPTION
-The Attribute Protocol is almost entirely an invention of this module. This is
-because Perl 5 does not have consistent notion of what is an attribute
-of a class. There are so many ways in which this is done, and very few
-(if any) are discoverable by this module.
+The Attribute Protocol is almost entirely an invention of this module,
+and is completely optional to this MOP. This is because Perl 5 does not
+have consistent notion of what is an attribute of a class. There are
+so many ways in which this is done, and very few (if any) are
+easily discoverable by this module.
So, all that said, this module attempts to inject some order into this
-chaos, by introducing a more consistent approach.
+chaos, by introducing a consistent API which can be used to create
+object attributes.
=head1 METHODS
=over 4
-=item B<new ($name, %accessor_description, $class_initialization_arg, $default_value)>
+=item B<new ($name, ?%options)>
+
+An attribute must (at the very least), have a C<$name>. All other
+C<%options> are contained added as key-valeue pairs. Acceptable keys
+are as follows:
+
+=over 4
+
+=item I<init_arg>
+
+This should be a string value representing the expected key in
+an initialization hash. For instance, if we have an I<init_arg>
+value of C<-foo>, then the following code will Just Work.
+
+ MyClass->meta->construct_instance(-foo => "Hello There");
+
+=item I<default>
+
+The value of this key is the default value which
+C<Class::MOP::Class::construct_instance> will initialize the
+attribute to.
+
+B<NOTE:>
+If the value is a simple scalar (string or number), then it can
+be just passed as is. However, if you wish to initialize it with
+a HASH or ARRAY ref, then you need to wrap that inside a CODE
+reference, like so:
+
+ Class::MOP::Attribute->new('@foo' => (
+ default => sub { [] },
+ ));
+
+ # or ...
+
+ Class::MOP::Attribute->new('%foo' => (
+ default => sub { {} },
+ ));
+
+If you wish to initialize an attribute with a CODE reference
+itself, then you need to wrap that in a subroutine as well, like
+so:
+
+ Class::MOP::Attribute->new('&foo' => (
+ default => sub { sub { print "Hello World" } },
+ ));
+
+And lastly, if the value of your attribute is dependent upon
+some other aspect of the instance structure, then you can take
+advantage of the fact that when the I<default> value is a CODE
+reference, it is passed the raw (unblessed) instance structure
+as it's only argument. So you can do things like this:
+
+ Class::MOP::Attribute->new('$object_identity' => (
+ default => sub { Scalar::Util::refaddr($_[0]) },
+ ));
+
+This last feature is fairly limited as there is no gurantee of
+the order of attribute initializations, so you cannot perform
+any kind of dependent initializations. However, if this is
+something you need, you could subclass B<Class::MOP::Class> and
+this class to acheive it. However, this is currently left as
+an exercise to the reader :).
+
+=back
+
+This I<accessor>, I<reader>, I<writer> and I<predicate> keys can
+contain either; the name of the method and an appropriate default
+one will be generated for you, B<or> a HASH ref containing exactly one
+key (which will be used as the name of the method) and one value,
+which should contain a CODE reference which will be installed as
+the method itself.
+
+=over 4
+
+=item I<accessor>
+
+The I<accessor> is a standard perl-style read/write accessor. It will
+return the value of the attribute, and if a value is passed as an argument,
+it will assign that value to the attribute.
+
+B<NOTE:>
+This method will properly handle the following code, by assigning an
+C<undef> value to the attribute.
+
+ $object->set_something(undef);
+
+=item I<reader>
+
+This is a basic read-only accessor, it will just return the value of
+the attribute.
+
+=item I<writer>
+
+This is a basic write accessor, it accepts a single argument, and
+assigns that value to the attribute. This method does not intentially
+return a value, however perl will return the result of the last
+expression in the subroutine, which returns in this returning the
+same value that it was passed.
+
+B<NOTE:>
+This method will properly handle the following code, by assigning an
+C<undef> value to the attribute.
+
+ $object->set_something();
+
+=item I<predicate>
+
+This is a basic test to see if the value of the attribute is not
+C<undef>. It will return true (C<1>) if the attribute's value is
+defined, and false (C<0>) otherwise.
+
+=back
=back
=head2 Informational
+These are all basic read-only value accessors for the values
+passed into C<new>. I think they are pretty much self-explanitory.
+
=over 4
=item B<name>
=item B<init_arg>
-=item B<default>
+=item B<default (?$instance)>
+
+As noted in the documentation for C<new> above, if the I<default>
+value is a CODE reference, this accessor will pass a single additional
+argument C<$instance> into it and return the value.
=back
=head2 Informational predicates
+These are all basic predicate methodfor the values passed into C<new>.
+
=over 4
=item B<has_accessor>
-Returns true if this attribute uses a get/set accessor, and false
-otherwise
-
=item B<has_reader>
-Returns true if this attribute has a reader, and false otherwise
-
=item B<has_writer>
-Returns true if this attribute has a writer, and false otherwise
-
=item B<has_predicate>
-Returns true if this attribute has a predicate, and false otherwise
-
=item B<has_init_arg>
-Returns true if this attribute has a class intialization argument, and
-false otherwise
-
=item B<has_default>
-Returns true if this attribute has a default value, and false
-otherwise.
-
=back
=head2 Attribute Accessor generation
=item B<install_accessors ($class)>
This allows the attribute to generate and install code for it's own
-accessor methods. This is called by C<Class::MOP::Class::add_attribute>.
+accessor/reader/writer/predicate methods. This is called by
+C<Class::MOP::Class::add_attribute>.
=item B<remove_accessors ($class)>
This allows the attribute to remove the method for it's own
-accessor. This is called by C<Class::MOP::Class::remove_attribute>.
+accessor/reader/writer/predicate. This is called by
+C<Class::MOP::Class::remove_attribute>.
=back
=item B<meta>
+This will return a B<Class::MOP::Class> instance which is related
+to this class.
+
+It should also be noted that B<Class::MOP> will actually bootstrap
+this module by installing a number of attribute meta-objects into
+it's metaclass. This will allow this class to reap all the benifits
+of the MOP when subclassing it.
+
=back
=head1 AUTHOR
projects / gitmo/Class-MOP.git / blobdiff