3.2.1 Interface Parameters

New interface parameters can be defined by listing them in the Interface block statement of an MDL model definition. Every MDL model can contain one Interface block statement which is initiated by using the Interface keyword followed by a list of parameter definitions enclosed in braces:

Interface {
   protection Parameter<type> name = initial_value;
}

The definition of a parameter itself consists of a sequence of the following elements:

• the optional protection field specifies if this interface parameter will be inherited by derived MDL classes. Possible values for this field are protected and private. The default protection assumed when this field is omitted is private. Parameters marked as protected will be inherited by derived classes, while private parameters are only members of the actual MDL class itself.

• the keyword Parameter

• an optional MDL parameter type specification (<type>) which consists of the MDL parameter type name enclosed in a pair of ``<>''. The type specification can be omitted if the actual type of the interface parameter is already determined by the initialization or linkage of the parameter.

• the name of the interface parameter

• the optional initial value can be any valid MDL statement with an appropriate result type preceded by the operator ``=''.

Interface parameters can be referred to within all methods of the MDL class by using the ``:'' qualifier.

Various definitions of interface parameters are demonstrated in Example 3.10.

Interface {
             Parameter<double>     x;
   private   Parameter<int>        y     = 1 + 2*3;
   protected Parameter<MdlString>  name  = "Hugo";
}

Example 3.10: Interface definition