control construct
(::)/1
Description
::Message
Sends a message to self. Can 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).
When the predicate used to answer the message is a meta-predicate, the calling context for the predicate meta-arguments is the object sending the message.
The lookups for the message declaration and the corresponding method are performed using a depth-first strategy. A message to self necessarily implies the use of dynamic binding but a caching mechanism is used to improve performance in subsequent messages. See the User Manual section on performance for details.
Modes and number of proofs
::+callable - zero_or_more
Errors
Message is a variable:instantiation_errorMessage is neither a variable nor a callable term:type_error(callable, Message)Message, with predicate indicator Name/Arity, is declared private:permission_error(access, private_predicate, Name/Arity)Message, with predicate indicator Name/Arity, is not declared:existence_error(predicate_declaration, Name/Arity)Examples
area(Area) :-
::width(Width),
::height(Height),
Area is Width * Height.