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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

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.. rst-class:: align-right

control construct

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

(::)/1

Description

::

::Message

Sends a message to :term:self. Can only be 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`).

When the predicate used to answer the message is a :term:meta-predicate, the :term:`calling context <predicate calling context>` for the predicate meta-arguments is the object sending the message.

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