Introducing non-IDL data types or classes

On occasion, you may want a new .idl file to reference some element that the SOM Compiler would not recognize, such as a user-defined class or an instance variable or attribute with a user-defined data type. You can reference such elements if they already exist in .h or .xh files that the SOM Compiler can #include with your new .idl file, as follows:

• To introduce a non-IDL class, insert an interface statement that is a forward reference to the existing user-defined class. It must precede the interface statement for the new class in the .idl file.

• To declare an instance variable or attribute that is not a valid IDL type, declare a dummy typedef preceding the interface declaration.

• In each case above, in the implementation section use a passthru statement to pass an #include statement into the language-specific binding file(s) of the new .idl file (a) for the existing user-defined class or (b) for the real typedef.

In the following example, the generic SOM type somToken is used in the .idl file for the user's types "myRealType" and "myStructType". The passthru statement then causes an appropriate #include statement to be emitted into the C/C++ binding file, so that the file defining types "myRealType" and "myStructType" will be included when the binding files process. In addition, an interface declaration for "myOtherClass" is defined as a forward reference, so that an instance of that class can be used within the definition of "myCurrentClass". The passthru statement also #includes the binding file for "myOtherClass":

typedef somToken myRealType;typedef somToken myStructType;

interface myOtherClass;

interface myCurrentClass : SOMObject {
. . .
        implementation {
                . . .
                myRealType myInstVar;
                attribute myStructType st1;
                passthru C_h =
                        ""
                        "#include <myTypes.h>"
                        "#include <myOtherClass.h>"
                        "";
        };
};

Note: See also the section "Using the tk_foreign TypeCode" in Chapter 7, "The Interface Repository Framework."