..
   This file is part of Logtalk <https://logtalk.org/>  
   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.


.. index:: pair: ::/1; Control construct
.. _control_send_to_self_1:

::/1
====

Description
-----------

::

   ::Message

Sends a message to :term:`self`. Can only used in the body of a predicate
definition. The argument should match a :ref:`public <directives_public_1>`
or :ref:`protected <directives_protected_1>` predicate of *self*. It may
also match a :ref:`private <directives_private_1>` predicate
if the predicate is within the scope of the object where the method
making the call is defined, if imported from a category, if used from
within a category, or when using private inheritance. When the predicate
is declared but not defined, the message simply fails (as per the
:term:`closed-world assumption`).

The lookups for the message declaration and the corresponding method are
performed using a depth-first strategy. A message to *self* necessarily
implies the use of :term:`dynamic binding` but a caching mechanism is used
to improve performance in subsequent messages. See the User Manual section
on :ref:`performance <performance_performance>` for details.

Modes and number of proofs
--------------------------

::

   ::+callable - zero_or_more

Errors
------

| Message is a variable:
|     ``instantiation_error``
| Message is neither a variable nor a callable term:
|     ``type_error(callable, Message)``
| Message, with predicate indicator Name/Arity, is declared private:
|     ``permission_error(access, private_predicate, Name/Arity)``
| Message, with predicate indicator Name/Arity, is not declared:
|     ``existence_error(predicate_declaration, Name/Arity)``

Examples
--------

::

   area(Area) :-
       ::width(Width),
       ::height(Height),
       Area is Width * Height.

.. seealso::

   :ref:`control_send_to_object_2`,
   :ref:`control_call_super_1`,
   :ref:`control_delegate_message_1`
