=head3 How do I make non-Moose constructors work with Moose?
-Usually the correct approach to subclassing a non Moose class is
+Usually the correct approach to subclassing a non-Moose class is
delegation. Moose makes this easy using the C<handles> keyword,
coercions, and C<lazy_build>, so subclassing is often not the
ideal route.
=head3 How do I tell Moose to use get/set accessors?
The easiest way to accomplish this is to use the C<reader> and
-C<writer> attribute options. Here is some example code:
+C<writer> attribute options:
has 'bar' => (
isa => 'Baz',
when creating these methods.
If you do not like this much typing, and wish it to be a default for your
-class, please see L<MooseX::FollowPBP>. This will allow you to write:
+classes, please see L<MooseX::FollowPBP>. This extension will allow you to
+write:
has 'bar' => (
isa => 'Baz',
is => 'rw',
);
-And have Moose create separate C<get_bar> and C<set_bar> methods
+Moose will create separate C<get_bar> and C<set_bar> methods
instead of a single C<bar> method.
NOTE: This B<cannot> be set globally in Moose, as that would break
-other classes which are built with Moose.
+other classes which are built with Moose. You can still save on typing
+by defining a new L<MyApp::Moose> that exports Moose's sugar and then
+turns on L<MooseX::FollowPBP>. See L<Moose::Cookbook::Extending::Recipe4>.
-=head3 How can I get Moose to inflate/deflate values in the accessor?
+=head3 How can I inflate/deflate values in accessors?
Well, the first question to ask is if you actually need both inflate
and deflate.
If you only need to inflate, then we suggest using coercions. Here is
some basic sample code for inflating a L<DateTime> object:
- subtype 'DateTime'
- => as 'Object'
- => where { $_->isa('DateTime') };
+ class_type 'DateTime';
coerce 'DateTime'
=> from 'Str'
has 'timestamp' => (is => 'rw', isa => 'DateTime', coerce => 1);
-This creates a custom subtype for L<DateTime> objects, then attaches
-a coercion to that subtype. The C<timestamp> attribute is then told
+This creates a custom type for L<DateTime> objects, then attaches
+a coercion to that type. The C<timestamp> attribute is then told
to expect a C<DateTime> type, and to try to coerce it. When a C<Str>
type is given to the C<timestamp> accessor, it will attempt to
coerce the value into a C<DateTime> object using the code in found
For a more comprehensive example of using coercions, see the
L<Moose::Cookbook::Basics::Recipe5>.
-If you need to deflate your attribute, the current best practice is to
-add an C<around> modifier to your accessor. Here is some example code:
+If you need to deflate your attribute's value, the current best practice
+is to add an C<around> modifier to your accessor:
# a timestamp which stores as
# seconds from the epoch
We limit C<before> and C<after> because this lets you write more
concise code. You do not have to worry about passing C<@_> to the
-original method, or forwarding its response (being careful to preserve
-context).
+original method, or forwarding its return value (being careful to
+preserve context).
-The C<around> method modifier has neither of these limitations.
+The C<around> method modifier has neither of these limitations, but
+is a little more verbose.
=head3 Can I use C<before> to stop execution of a method?
modifier is the only modifier which can gracefully prevent execution
of the main method. Here is an example:
- around 'baz' => sub {
- my $next = shift;
- my ($self, %options) = @_;
- unless ($options->{bar} eq 'foo') {
- return 'bar';
- }
- $next->($self, %options);
- };
+ around 'baz' => sub {
+ my $next = shift;
+ my ($self, %options) = @_;
+ unless ($options->{bar} eq 'foo') {
+ return 'bar';
+ }
+ $next->($self, %options);
+ };
By choosing not to call the C<$next> method, you can stop the
execution of the main method.
=head2 Type Constraints
-=head3 How can I have a custom error message for a type constraint?
+=head3 How can I provide a custom error message for a type constraint?
-Use the C<message> option when building the subtype, like so:
+Use the C<message> option when building the subtype:
subtype 'NaturalLessThanTen'
=> as 'Natural'
=> where { $_ < 10 }
=> message { "This number ($_) is not less than ten!" };
-This will be called when a value fails to pass the C<NaturalLessThanTen>
-constraint check.
+This C<message> block will be called when a value fails to pass the
+C<NaturalLessThanTen> constraint check.
=head3 Can I turn off type constraint checking?
-Not yet. This option will likely be coming in a future release.
+Not yet. This option will likely come in a future release.
=head2 Roles
=head3 How do I get Moose to call BUILD in all my composed roles?
-See L<Moose::Cookbook::WTF> and specifically the B<Why is BUILD
-not called for my composed roles?> question in the B<Roles> section.
+See L<Moose::Cookbook::WTF> and specifically the
+B<Why is BUILD not called for my composed roles?> question in the
+B<Roles> section.
=head3 What are Traits, and how are they different from Roles?
In Moose-speak, a I<Role> is usually composed into a I<class> at
compile time, whereas a I<Trait> is usually composed into an instance
-of a class at runtime to add or modify the behavior of B<just that
-instance>.
+of a class at runtime to add or modify the behavior of
+B<just that instance>.
Outside the context of Moose, traits and roles generally mean exactly the
same thing. The original paper called them Traits, however Perl 6 will call
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