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super_calls

This simple programming example illustrates that super calls (the (^^)/1 control construct) preserve the value of self when calling an inherited definition. This allows any (::)/1 goal in the called inherited definition to work as expected in the correct context. This example also illustrates that super calls require dynamic binding when the called predicate is dynamic.

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

%versions

Start by loading the example:

logtalk_load(super_calls(loader)).

The predicate get_local/1 calls the local/1 predicate in self, i.e. in the object that receives the get_local/1 message:

parent::get_local(Local).

<!-- Local = parent. -->

prototype::get_local(Local).

<!-- Local = prototype. -->

The `prototype::correct/1` predicate makes a super call, which preserves self, to the inherited get_local/1 predicate:

prototype::correct(Local).

<!-- Local = prototype. -->

The `prototype::wrong/1` predicate sends a message to the parent, which (necessarily) resets self to the message receiver:

prototype::wrong(Local).

<!-- Local = parent. -->

The super calls force dynamic binding when the called predicate is dynamic:

bottom::value(Value).

<!-- Value = parent. -->

middle::assertz(d(middle)).

<!-- true. -->

bottom::value(Value).

<!-- Value = middle. -->

middle::retractall(d(_)).

<!-- true. -->

bottom::value(Value).

<!-- Value = parent. -->