[omniORB] Question about unions and c++ mapping

[david.jobet at americas.bnpparibas.com]

Hello,

I have read the "Mapping for Union Types" available on the omg website 
http://www.omg.org/spec/CPP/1.2/PDF/
(and honestly I'm not sure I understand it completly)

Here's an IDL I have to use :

  enum MyEnum
  {
    myEnum1,
    myEnum2
  };

  union MyUnion switch(MyEnum)
  {
    case myEnum1: LightweightObject lightweight;
    case myEnum2: FatObject fat;
  };

I don't have a control over it and I need to allocate a sequence of it 
(possibly long).

Basically, this is what I would like to write : (#1)
  MyUnion &union = seq[no]; // seq is a sequence of MyUnion
  union._d(myEnum2); // oops, discriminant not initialized yet
  FatObject &fat = union.fat();
  initializeFat(fat);

But it does not work, the correct compliant way is : (#2)
  MyUnion &union = seq[no]; // seq is a sequence of MyUnion
  FatObject fat;
  initializeFat(fat);
  union.fat(fat); // initialize discriminant and performs deep copy

Is there any way to avoid the deep copy ? It can be costly if the sequence 
is very long.
Is there any good reason the spec disallow writing code #1 ?

Looking at the code generated by omniidl, it would be completly possible 
and safe to do it in the #1 way, but I would have to manually patch the 
generated code to explictly allow it.
Any thought about it ?

Tx

David


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