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# reflection

Run this example with no other examples loaded at the same time.

This folder contains an example that shows how to implement a reflective
class-based system. There are three main classes:

- `object`  
	root of the inheritance graph
- `class`  
	default metaclass for all instantiable classes
- `abstract_class`  
	default metaclass for all abstract classes

Each class inherit all the methods form the other two classes and from 
itself (without any inheritance loops of course ;-).

You can find more sophisticated versions of these classes in the `roots`
example. If you are not familiar with the concept of metaclass used in
this example, see the `metaclasses` example first.

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

```logtalk
%versions
```

Start by loading the example:

```logtalk
logtalk_load(reflection(loader)).
```

Print the (public and protected) interface of each class:

```logtalk
object::print, abstract_class::print, class::print.
```

<!--
Object: object

  interface:
    new/1
    delete/1
    instances/1
    metaclass/0
    abstract_class/0
    strict_instance/0
    print/0

Object: abstract_class

  interface:
    new/1
    delete/1
    instances/1
    metaclass/0
    abstract_class/0
    strict_instance/0
    print/0

Object: class

  interface:
    new/1
    delete/1
    instances/1
    metaclass/0
    abstract_class/0
    strict_instance/0
    print/0

true.
-->

The object `Class` is the metaclass of all classes:

```logtalk
class::instances(Instances), class::metaclass.
```

<!--
Instances = [class,abstract_class,object].
-->

Create an abstract class, check it and print its interface:

```logtalk
abstract_class::new(ac), ac::abstract_class, ac::print.
```

<!--
Object: ac

  interface:
    metaclass/0
    abstract_class/0
    strict_instance/0
    print/0

true.
-->

Try to create an instance of the abstract class:

```logtalk
catch(ac::new(i), Error, true).
```

<!--
Error = error(existence_error(predicate_declaration,new(i)),ac::new(i),user).
-->

Create a new instantiable class and print its interface:

```logtalk
class::new(c), c::print.
```

<!--
Object: c

  interface:
    new/1
    delete/1
    instances/1
    metaclass/0
    abstract_class/0
    strict_instance/0
    print/0

true.
-->

Create an instance of the new class:

```logtalk
c::new(i), c::instances(Instances).
```

<!--
Instances = [i].
-->

Because `c` does not declare any predicates, its instances have no interface:

```logtalk
\+ i::current_predicate(_).
```

<!--
true.
-->

Create an instance of object, root of the inheritance graph, and print its interface:

```logtalk
object::new(j), j::print.
```

<!--
Object: j

  interface:
    strict_instance/0
    print/0

true.
-->

Delete the dynamic objects that we created:

```logtalk
c::delete(i), class::delete(c), abstract_class::delete(ac), object::delete(j).
```

<!--
true.
-->
