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.. rst-class:: align-right

built-in method

.. index:: pair: before/3; Built-in method .. _methods_before_3:

before/3

Description

::

before(Object, Message, Sender)

User-defined method for handling :ref:`before events <events_definitions>`. This method is declared in the :ref:`monitoring apis:monitoring/0` built-in protocol as a public predicate and is automatically called by the runtime for messages sent using the :ref:control_send_to_object_2 control construct from within objects compiled with the :ref:`events <flag_events>` flag set to allow.

Note that you can make this predicate scope protected or private by using, respectively, :ref:`protected or private implementation <inheritance_scope>` of the monitoring protocol.

Modes and number of proofs

::

before(?object_identifier, ?callable, ?object_identifier) - zero_or_more

Errors

(none)

Examples

::

:- object(..., implements(monitoring), ...).

% write a log message when a message is sent: before(Object, Message, Sender) :- writeq(Object), write('::'), writeq(Message), write(' from '), writeq(Sender), nl.

.. seealso::

:ref:methods_after_3, :ref:predicates_abolish_events_5, :ref:predicates_current_event_5, :ref:predicates_define_events_5