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complements (allow)

This folder contains an example that show how to use both static and dynamic categories to explicitly complement an existing object compiled with the complements flag set to allow. With this setting, a category can both redefine and add new functionality to the complemented object.

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

%versions

Start by loading the non-patched employee object:

logtalk_load(complements_allow(employee)).

Ask the employee object its name:

employee::name(Name).

<!-- Name = john. -->

Ask the employee object its salary:

employee::salary(Salary).

<!-- Salary = 23500. -->

Check the protocol of the employee object:

findall(Predicate, employee::current_predicate(Predicate), Predicates).

<!-- Predicates = [age/1, name/1, salary/1]. -->

Now load the add_on complementing category:

logtalk_load(complements_allow(add_on)).

Load the `dynamic.lgt` source file that creates a dynamic complementing category, also patching the employee object:

logtalk_load(complements_allow(dynamic)).

Find categories that complement objects:

%%table
complements_object(Category, Object).

<!-- Category = dynamic_patch, Object = employee ; Category = add_on, Object = employee ; false. -->

Use the event handler defined in the add_on category for the employee object:

employee::name(Name).

<!-- Received message name(_16) from user Name = john. -->

Check the consequences of the runtime patch of the salary/1 predicate:

employee::salary(Salary).

<!-- Received message salary(_G192) from user Salary = 42000. -->

Check the new protocol of the employee object:

employee::predicates(Predicates).

<!-- Received message predicates(_G180) from user

Predicates = [after/3, age/1, before/3, income/1, name/1, predicates/1, salary/1]. -->

List the properties of the predicates/1 predicate:

%%table
employee::predicate_property(predicates(_), Property).

<!-- Property = logtalk ; Property = scope(public) ; Property = (public) ; Property = static ; Property = declared_in(add_on) ; Property = declared_in(add_on, 29) ; Property = defined_in(add_on) ; Property = defined_in(add_on, 31) ; Property = number_of_clauses(1). -->

List the properties of the income/1 predicate:

%%table
employee::predicate_property(income(_), Property).

<!-- Property = logtalk ; Property = scope(public) ; Property = (public) ; Property = static ; Property = declared_in(employee) ; Property = alias_of(salary(_G3724)) ; Property = defined_in(dynamic_patch) ; Property = number_of_clauses(0). -->

Later, the boss finds out about the employee hacked salary:

abolish_category(dynamic_patch).

<!-- true. -->

The employee salary is thus back to its original value:

employee::salary(Salary).

<!-- Received message salary(_G192) from user Salary = 23500. -->