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# delegates

This folder contains an implementation of the delegation design pattern and
is based on the sample code found on the Rosetta Code website. For more
information see:

http://en.wikipedia.org/wiki/Delegation_pattern

http://rosettacode.org/wiki/Delegates#Logtalk

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

```logtalk
%versions
```

Load the example:

```logtalk
logtalk_load(delegates(loader)).
```

Without a delegate:

```logtalk
a_delegator::operation(String).
```

<!--
String = 'default implementation'.
-->

With a delegate that does not implement `thing/1`:

```logtalk
a_delegator::set_delegate(an_object), a_delegator::operation(String).
```

<!--
String = 'default implementation'.
-->

With a delegate that implements `thing/1`:

```logtalk
a_delegator::set_delegate(a_delegate), a_delegator::operation(String).
```

<!--
String = 'delegate implementation'.
-->

Same queries but using the parametric object implementation:

```logtalk
a_delegator(an_object)::operation(String).
```

<!--
String = 'default implementation'.
-->

```logtalk
a_delegator(a_delegate)::operation(String).
```

<!--
String = 'delegate implementation'
-->
