A function used to convert values flowing through associations. For interface objects of mode in, conversion functions are allowed only on actuals. For interface objects of mode out or buffer, conversion functions are allowed only on formals. For interface objects of mode inout or linkage, conversion functions are allowed on both formals and actuals. Conversion functions have a single parameter. A conversion function associated with an actual accepts the type of the actual and returns the type of the formal. A conversion function associated with a formal accepts the type of the formal and returns the type of the actual.