built-in method

# `this/1`

## Description

    this(This)

Unifies its argument with the identifier of the object calling this method. When this method is called from a category, the argument is unified with the object importing the category on whose behalf the clause containing the call is being used to prove the current goal.

This private method is implemented as a unification between its argument and the corresponding implicit execution-context argument in the predicate clause making the call. This unification occurs at the clause head when the argument is not bound at compile-time (the most common case).

This method is useful for avoiding hard-coding references to an object identifier or for retrieving all object parameters with a single call when using parametric objects.

## Modes and number of proofs

    this(?object_identifier) - zero_or_one

## Errors

(none)

## Examples

    % after compilation, the write/1 call will
    % be the first goal in the clause body
    test :-
        this(This),
        write('Using a predicate clause contained in '),
        writeq(This), nl.

See also

context/1, parameter/2, self/1, sender/1