Logtalk reference manual
Entity directive: uses/2
Contents > Reference Manual > Directives > uses/2

## uses/2

#### Description

    uses(Object, Predicates)
    uses(Object, PredicatesAndAliases)

    uses(Object, NonTerminals)
    uses(Object, NonTerminalsAndAliases)

Declares that all calls (made from predicates defined in the category or object containing the directive) to the specified predicates are to be interpreted as messages to the specified object. Thus, this directive may be used to simplify writing of predicate definitions by allowing the programmer to omit the `Object::` prefix when using the predicates listed in the directive (as long as the predicate calls do not occur as arguments for non-standard Prolog meta-predicates not declared on the adapter files). It is also possible to include operator declarations, `op(Precedence, Associativity, Operator)`, in the second argument.

This directive is also used when compiling calls to the database and reflection built-in methods by looking into these methods predicate arguments.

It is possible to specify a predicate alias using the notation `Functor/Arity as Alias/Arity` or, in alternative, the notation `Functor/Arity::Alias/Arity`. Aliases may be used either for avoiding conflicts between predicates specified in `use_module/2` and `uses/2` directives or for giving more meaningful names considering the using context of the predicates.

To enable the use of static binding, and thus optimal message sending performance, the objects should be loaded before compiling the entities that call their predicates.

#### Template and modes

    uses(+object_identifier, +predicate_indicator_list)
    uses(+object_identifier, +predicate_indicator_alias_list)

    uses(+object_identifier, +non_terminal_indicator_list)
    uses(+object_identifier, +non_terminal_indicator_alias_list)

#### Examples

    :- uses(list, [append/3, member/2]).
    :- uses(store, [data/2]).

    foo :-
        ...,
        findall(X, member(X, L), A),    % the same as findall(X, list::member(X, L), A)
        append(A, B, C),                % the same as list::append(A, B, C)
        assertz(data(X, C)),            % the same as store::assertz(data(X, C))
        ...

Another example, using the extended notation that allows us to define predicate aliases:

    :- uses(btrees, [new/1::new_btree/1]).
    :- uses(queues, [new/1::new_queue/1]).

    btree_to_queue :-
        ...,
        new_btree(Tree),     % the same as btrees::new(Tree)
        new_queue(Queue),    % the same as queues::new(Queue)
        ...

#### See also

`use_module/2`