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.. This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2024 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0
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 .. _call_in_this_1:
(@)/1
::
@Predicate
Calls a predicate definition in :term:this
. The argument must be a callable
term at compile time. The predicate must be declared (by a scope directive).
This control construct provides access to predicate definitions in this from
categories. For example, it allows overriding a predicate definition from a
complementing category with a new definition that calls goals before and
after calling the overriden definition (the overriding definition is sometimes
described in other programming languages as an around method). When used
within an object, it's the same as calling its argument.
::
@ +callable - zero_or_more
| Predicate
, with predicate indicator Name/Arity
, is not declared:
| existence_error(predicate_declaration, Name/Arity)
Assuming an object declaring a make_sound/0 predicate, define an around method in a complementing category:
::
make_sound :-
write('Started making sound...')
, nl,
@make_sound,
write('... finished making sound.')
, nl.
.. seealso::
:ref:control_send_to_object_2
,
:ref:control_send_to_self_1
,
:ref:control_delegate_message_1