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{{Preliminary Documentation}}

{{languageReferenceNavbar|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 ===

<vipbnf><Attributes> :
    [ <Attribute>-comma-sep-list ]</vipbnf>

<vipbnf><Attribute> : one of
    <LowerCaseIdentifier>
    <LowerCaseIdentifier> ( <Literal>-comma-sep-list )</vipbnf>

Where the literals must either be numbers or string literals.

=== Insertion Points ===

The attributes of interfaces, classes and implementations is right before the scope qualifications.

<vipbnf><InterfaceDeclaration> :
   interface <IinterfaceName> <Attributes>-opt <ScopeQualifications> <Sections> end interface <IinterfaceName>-opt</vipbnf>

<vipbnf><ClassDeclaration> :
   class <ClassName> <ConstructionType>-opt <Attributes>-opt <ScopeQualifications> <Sections> end class <ClassName>-opt</vipbnf>

<vipbnf><ClassImplementation> :
   implement <ClassName> <Attributes>-opt <ScopeQualifications> <Sections> end implement <ClassName>-opt</vipbnf>

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

<vipbnf><ConstantDefinition>: one of
    <ConstantName> = <ConstantValue> <Attributes>-opt
    <ConstantName> : <TypeName> = <ConstantValue> <Attributes>-opt</vipbnf>

<vipbnf><DomainDefinition>:
    <DomainName> <FormalTypeParameterList>-opt = <TypeExpression> <Attributes>-opt</vipbnf>

<vipbnf><PredicateDeclaration> :
   <PredicateName> : <PredicateDomain> <LinkName>-opt <Attributes>-opt
   <PredicateName> : <PredicateDomainName> <LinkName>-opt <Attributes>-opt</vipbnf>

<vipbnf><PropertyDeclaration> :
    <PropertyName> : <PropertyType> <FlowPattern>-list-opt <Attributes>-opt</vipbnf>

<vipbnf><FactDeclaration> :
   <FactVariableDeclaration> <Attributes>-opt
   <FactFunctorDeclaration> <Attributes>-opt</vipbnf>

The attributes of formal arguments is at the end.

<vipbnf><FormalArgument> :
    <TypeExpression> <ArgumentName>-opt <Attributes>-opt</vipbnf>

=== Specific Attributes ===

==== byVal ====

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

{{Example|
<vip>predicates
    externalP : (point Point [byVal]) language apicall.</vip>
}}

==== 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|
<vip>predicates
    oldFasioned : (string Arg) [deprecated("Use newFasion instead")].</vip>
}}

==== formatString ====

The argument is a format string for a subsequent elipsis argument (i.e. <vp>...</vp>).  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|
<vip>predicates
    writef : (string Format [formatString], ...).</vip>
}}

==== in ====

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

{{Example|
<vip>predicates
    pred : (string InputArg [in]).</vip>
}}

==== 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|
<vip>domains
    point = align 4 
        p(integer X, integer Y).

domains
    rectangle = align 4
        r(
            point UpperLeft [inline],
            point LowerRight [inline]
        ).</vip>
}}


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

{{Example|
<vip>domains
    device = align 4
        device(
            integer Id,
            string DeviceName [inline(32)]
        ).</vip>
}}

==== 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 constructors at all.  Valid for a object creating class declaration.

{{Example|
<vip>class classWithoutPublicConstructors : myInterface
    [noDefaultConstructor]
...
end class classWithoutPublicConstructors</vip>
}}

==== out ====

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

{{Example|
<vip>predicates
    pred : (string OutputArg [out]).</vip>
}}

==== retired ====

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

{{Example|
<vip>predicates
    veryOldFasioned : (string Arg) [retired("Use newFasion instead")].</vip>
}}


==== union ====

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

{{Example|
<vip>domains
    u64var = 
        u64(unsigned64 Value64);
        u64_struct(unsigned Low32, unsigned High32)
        [union].</vip>
}}


==== used ====

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

{{Example|
<vip>predicates
    seeminglyUnused : () [used].</vip>
}}

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