Language Reference/Attributes

Various definitions and declarations can be annotated with attributes. This section describes the general syntax of attributes and where they can be placed. It also describes the meaning of the specific attributes.

Syntax

Attributes :
    [ Attribute-comma-sep-list ]

Attribute : one of
    LowerCaseIdentifier
    LowerCaseIdentifier ( Literal-comma-sep-list )

where the literals must either be numbers or string literals.

Insertion Points

The attributes of interfaces, classes and implementations are right after the scope qualifications.

InterfaceDeclaration :
    interface IinterfaceName
        ScopeQualifications
        Attributes-opt
    Sections
end interface IinterfaceName-opt

ClassDeclaration :
    class ClassName ConstructionType-opt
        ScopeQualifications
        Attributes-opt
    Sections
    end class ClassName-opt

ClassImplementation :
   implement ClassName
        ScopeQualifications
        Attributes-opt
    Sections
    end implement ClassName-opt

The attributes of constants, domains, predicates, properties and facts are at the end (i.e. right before the terminating dot).

ConstantDefinition: one of
    ConstantName = ConstantValue Attributes-opt
    ConstantName : TypeName = ConstantValue Attributes-opt

DomainDefinition:
    DomainName FormalTypeParameterList-opt = TypeExpression Attributes-opt

PredicateDeclaration :
    PredicateName : PredicateDomain LinkName-opt Attributes-opt
    PredicateName : PredicateDomainName LinkName-opt Attributes-opt

PropertyDeclaration :
    PropertyName : PropertyType FlowPattern-list-opt Attributes-opt

FactDeclaration :
    FactVariableDeclaration Attributes-opt
    FactFunctorDeclaration Attributes-opt

The attributes of formal arguments are at the end.

FormalArgument :
    TypeExpression ArgumentName-opt Attributes-opt

Specific Attributes

byVal

An argument is transferred directly on the stack rather than using a pointer. Valid for formal predicate arguments provided the language is stdcall, apicall or c.

Example

predicates
    externalP : (point Point [byVal]) language apicall.

deprecated

The declared entity is deprecated. The string literal describes how to migrate from it. The entity still exist, but usage will cause a warning. The entity will not exist in future versions of Visual Prolog. Valid for member declarations and scopes.

Example

predicates
    oldFasioned : (string Arg) [deprecated("Use newFasion instead")].

formatString

The argument is a format string for a subsequent ellipsis argument (i.e. ...). Valid for one string argument of a predicate with an ellipsis argument. The use of formatString will make the compiler check the validity of actual arguments with respect to actual format strings (where possible).

Example

predicates
    writef : (string Format [formatString], ...).

in

The argument is an input argument. Valid for a formal predicate argument.

Example

predicates
    pred : (string InputArg [in]).

inline

inline alters the memory layout of a struct (i.e. a single alternative functor domain with an align qualification). The corresponding field is inlined instead of being pointed to.

Example

domains
    point = align 4
        p(integer X, integer Y).
 
domains
    rectangle = align 4
        r(
            point UpperLeft [inline],
            point LowerRight [inline]
        ).

It is also possible to inline fixed size string and string8 fields in structs:

Example

domains
    device = align 4
        device(
            integer Id,
            string DeviceName [inline(32)]
        ).

noDefaultConstructor

Used for a class to indicate that it should not have an implicit default constructor, and can thus be used to a class that does not have any public constructors at all. Valid for an object creating class declaration.

Example

class classWithoutPublicConstructors : myInterface
    [noDefaultConstructor]
...
end class classWithoutPublicConstructors

out

The argument is an output argument. Valid for a formal predicate argument.

Example

predicates
    pred : (string OutputArg [out]).

programPoint

Used for a predicate or constructor declaration to indicate that it recieves an extra input argument which describes the place in a program (program point) where this predicate was called. This additional argument has programPoint type which is declared in the PFC core class like:

domains
    programPoint = programPoint(hScopeDescriptor ClassDescriptor, string PredicateName, sourceCursor Cursor).

The clause name of such predicate or constructor should have suffix "_explicit". Valid for a predicate or constructor declaration.

Example

predicates
    pred : (string String) [programPoint].
clauses
    pred_explicit(ProgramPoint, String) :-
        ...

The programPoint attribute is described in more details in the description of Predicates, and it is a vital part of the exception system, see Exception Handling.

retired

The declared entity is retired. The string literal describes how to migrate from it. The entity does not exist anymore.

Example

predicates
    veryOldFasioned : (string Arg) [retired("Use newFasion instead")].

sealed

Used for an interface to indicate that it cannot be supported by any other interface. This allows to create more efficient codes, because the compiler provides some optimization when using the objects of such type. Valid for an object creating class declaration as a construction interface.

Example

interface myInterface
    [sealed]
...
end interface myInterface
 
class myClass : myInterface
...
end class myClass

union

Used for creating functor domains with several alternatives but no real functors. This should only be used to mimic C/C++ union structs in low-level interfacing. Valid for functor domain with several alternatives and alignment.

Example

domains
    u64var = align 4
        u64(unsigned64 Value64);
        u64_struct(unsigned Low32, unsigned High32)
        [union].

used

An unused local member can be marked used to prevent the compiler to issue a warning and remove the corresponding code. Valid for members.

Example

predicates
    seeminglyUnused : () [used].