[coyotos-dev] Position statement on IDL bindings

[Jonathan S. Shapiro]

So here is my final outcome on all of this:

0. While C++ should be able to call the C binding, there is no intrinsic
   reason why C++ should be restricted to the C binding. It is feasible
   for C++ to have a distinct binding. It is even feasible for both the
   C and the C++ bindings to be accessible for use by C++ code
   simultaneously, which supports the case where existing "C++ safe" C
   code is being compiled using the C++ compiler.

1. For languages that have native exception handling, IDL exceptions
   should turn in to language exceptions, and the nominal return type
   of the method should be used as the return type of the stub
   procedure.

   In the case of procedures returning capabilities, the preferred
   implementation will be one of the following:

     A. Rotate the return value to the end of the parameter list
        as an OUT parameter and change the return type to void.

        This is an appropriate simple implementation for C++, for
        example.

     B. Provide a means, possibly through the IdlEnvironment mechanism
        to "allocate" an appropriate location for the return capability.

        In this type of binding, the location can be "allocated"
        before the call, and the encapsulating language object can
        then be returned as the return value.

   Which solution is appropriate is highly language dependent. In a
   GC'd language, for example, the approach of allocating locations
   is probably preferred. In C++, it is possible to imagine an
   encapsulating template that uses reference counting on capability
   locations.

2. For languages that do NOT have native exception handling, IDL
   result codes should be returned by the stub, and the nominal return
   type (if not void) should be rotated to the end of the parameter
   list.

   This averts certain initialization errors, and makes error checking
   simpler and more consistent.

3. For compatibility with existing CORBA-based C code, provide a new
   back end for the existing IDL compiler. Solve the problem of
   capability return values by rotating those to the last parameter
   position. Otherwise use the binding currently used by those
   environments.

-- 
Jonathan S. Shapiro, Ph.D.
Managing Director
The EROS Group, LLC