::/2

Description

Object::Message
{Proxy}::Message

Sends a message to an object. The message argument must match a public predicate of the receiver object. When the message corresponds to a protected or private predicate, the call is only valid if the sender matches the predicate scope container. When the predicate is declared but not defined, the message simply fails (as per the closed-world assumption).

The {Proxy}::Message syntax allows simplified access to parametric object proxies. Its operational semantics is equivalent to the goal conjunction (call(Proxy), Proxy::Message). I.e. Proxy is proved within the context of the pseudo-object user and, if successful, the goal term is used as a parametric object identifier. Exceptions thrown when proving Proxy are handled by the ::/2 control construct. This construct construct supports backtracking over the {Proxy} goal.

The lookups for the message declaration and the corresponding method are performed using a depth-first strategy. Depending on the value of the optimize flag, these lookups are performed at compile time whenever sufficient information is available. When the lookups are performed at runtime, 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

+object_identifier::+callable - zero_or_more
{+object_identifier}::+callable - zero_or_more

Errors

Either Object or Message is a variable:
instantiation_error
Object is neither a variable nor a valid object identifier:
type_error(object_identifier, Object)
Message 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 declared protected:
permission_error(access, protected_predicate, Name/Arity)
Message, with predicate indicator Name/Arity, is not declared:
existence_error(predicate_declaration, Name/Arity)
Object does not exist:
existence_error(object, Object)

Proxy is a variable:
instantiation_error
Proxy is neither a variable nor a callable term:
type_error(callable, Proxy)
Proxy, with predicate indicator Name/Arity, does not exist in the user pseudo-object:
existence_error(procedure, Name/Arity)

Examples

| ?- list::member(X, [1, 2, 3]).

X = 1 ;
X = 2 ;
X = 3
yes

See also

::/1, ^^/1, []/1