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around_methods

This example illustrates how to use a complementing category to define what is often described as an "around method". It uses the @/1 control construct that allows calling the original predicate definition (in the patched object) from its new definition in the category. This control construct allows the new definition to call some goals, followed by a call to the original definition, followed by calls to some more goals, hence the name "around method".

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the unpatched object:

logtalk_load(around_methods(bird)).

Call the unpatched `bird::make_sound/0` predicate:

bird::make_sound.

<!-- Chirp, chirp!

true. -->

Next load the complementing category defining the patch for the `bird::make_sound/0` predicate:

logtalk_load(around_methods(patch)).

Call the now patched `bird::make_sound/0` predicate:

bird::make_sound.

<!-- Started making sound... Chirp, chirp! ... finished making sound.

true. -->