Delegation
Delegation is yet
another
possible relationship between an object and another body of code.
Rather than pull methods into a class, you call methods in another
object as if they were methods of the class. In Perl 6, delegation
can be done in either a class or a role. A delegated object is simply
an attribute defined in the class or role. The
handles
keyword specifies which methods of the delegated object will act as
methods of the class. This example declares that any calls to the
thumb_ride
method on an object with the
Hitchhiker
role, will actually call the method on
its $.thumb
attribute:
role Hitchhiker { . . . has Electronic::Thumb $.thumb handles 'thumb_ride'; . . . }
The handles
keyword accepts many variations in the
syntax to delegate methods. You can
pass it an array reference of multiple method names:
has Electronic::Thumb $.thumb handles ['thumb_ride', 'sub_etha'];
or a quoted list:
has Electronic::Thumb $.thumb handles «thumb_ride sub_etha»;
A pair in place of a string method name gives the method a different
name in the class. This example declares a method named
hitch
in the class, but any calls to it are
delegated to the thumb_ride
method on the
$.thumb
object:
has Electronic::Thumb $.thumb handles :hitch«thumb_ride»;
If the method name is given as a pattern, it’s a
wildcard delegation and all methods
that match that pattern will be delegated to the attribute. This
example delegates all methods that start with
“thumb” to
$.thumb
:
has Electronic::Thumb $.thumb ...
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