Logtalk reference manual
Control construct: ::/1
Contents > Reference Manual > Control Constructs > ::/1

## ::/1

#### Description

    ::Message

Send a message to self. Only used in the body of a predicate definition. The argument should match a public or protected predicate of self. It may also match a private predicate if the predicate is within the scope of the object where the method making the call is defined, if imported from a category, if used from within a category, or when using private inheritance. When the predicate is declared but not defined, the message simply fails (as per the closed-world assumption).

The lookups for the message declaration and the corresponding method are performed using a depth-first strategy. A message to self necessarily requires the use of dynamic binding but a caching mechanism is used to improve performance in subsequent messages.

#### Template and modes

    ::+callable

#### Errors

Message is a variable:
  `instantiation_error`
Message is neither a variable nor a callable term:
  `type_error(callable, Message)`
Message, with predicate indicator Functor/Arity, is declared private:
  `permission_error(access, private_predicate, Functor/Arity)`
Message, with predicate indicator Functor/Arity, is not declared:
  `existence_error(predicate_declaration, Functor/Arity)`

#### Examples

    area(Area) :-
        ::width(Width),
        ::height(Height),
        Area is Width*Height.