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# patching

This folder contains an example that shows how to use a complementing
category to patch broken object predicate declarations and definitions 
(without modifying its source code), thus providing functionality similar
to Objective-C categories.

The complemented objects must be compiled with the flag `complements` set
to `allow` (its default value is usually `deny`). This solution was adapted
to improve performance of applications that don't make use complementing
categories and to provide a solution for preventing the use of categories
to break object encapsulation. Note that the `complements` flag can be set
on a per-object basis by using the `set_logtalk_flag/2` directive.

Start by loading the example:

```logtalk
logtalk_load(patching(loader)).
```

<!--
true.
-->

Find categories that complement objects:

```logtalk
complements_object(Category, Object).
```

<!--
Category = patch, Object = broken.
-->

Verify the patch in the `patch` category for the predicate `is_proper_list/1`
defined in the object "broken":

```logtalk
broken::is_proper_list([1,2,3]).
```

<!--
true.
-->

```logtalk
broken::is_proper_list(_).
```

<!--
false.
-->

```logtalk
broken::is_proper_list([a,b,c|_]).
```

<!--
false.
-->

Verify the patch in the `patch` category for the wrong scope of the `last/3`
predicate declared in the object `broken`:

```logtalk
broken::last(_, _, _).
```

<!--
    permission_error(access, private_predicate, last/3),
    broken::last(_, _, _),
    user)
-->

Verify the patch in the `patch` category for the wrong scope of the `last/3`
predicate declared in the object `broken`:

```logtalk
broken::nextto(2, 3, [1,2,3]).
```

<!--
true.
-->
