[xsde-users] XSDE : choice_arm function code generation question

[Boris Kolpackov]

Yegnaram, Shrikant <SYegnaram at cls-bank.com> writes:

>     union
>     {
>       union
>       {
>         size_t align_;
>         char data_[sizeof (::xmlevents::XYZ_CONTROL_CLASS)];
>       } control_;
>       ::xmlevents::XYZ_COM_INPUT_CLASS* comInput_;
>       ::xmlevents::ABC_INPUT_CLASS* abcInputClass_;
>       ::xmlevents::XYZ_NOTIFICATION_CLASS* notification_;
>     }
>
> [...]
> 
>   void XYZMessageClass::
>   choice_arm (choice_arm_tag x)
>   {
>     if (this->choice_arm_ == x)
>       return;
> 
>     switch (this->choice_arm_)
>     {
>       case control_tag:
>       {
>         typedef ::xmlevents::XYZ_CONTROL_CLASS _dtor;
>         reinterpret_cast< ::xmlevents::XYZ_CONTROL_CLASS& > (this->choice_.control_).~_dtor ();
>         break;
>       }
>       case comInput_tag:
>       {
>         delete this->choice_.comInput_;
>         break;
>       }
>       case abcInputClass_tag:
>       {
>         delete this->choice_.abcInputClass_;
>         break;
>       }
> 
>      ...
> 
>     this->choice_arm_ = choice_arm_tag (57);
> 
>     switch (x)
>     {
>       case control_tag:
>       {
>         new (&this->choice_.control_) ::xmlevents::XYZ_CONTROL_CLASS;
>         break;
>       }
>       case comInput_tag:
>       {
>         this->choice_.comInput_ = 0;
>         break;
>       }
>       case abcInputClass_tag:
>       {
>         this->choice_.abcInputClass_ = 0;
>         break;
>       }
> 
>     ...
> 
>     this->choice_arm_ = x;
> }
> 
> 
> The question here is regarding elements like XYZMessage.comInput are
> not allocated / deallocated  memory in the choice_arm function like
> XYZMessage.control field.

The difference is due to whether the type is fixed or variable-length.
This is covered in Section 4.2, "Memory Management":

https://codesynthesis.com/projects/xsde/documentation/cxx/hybrid/guide/#4.2


>   1.  Why is XSDE creating union {align,data_} for some of the classes
>       in the xs:choice and not for others? We would like to understand
>       this better.

This is due to the fixed vs variable-length distinction.


>   2.  If we can change the default behaviour to generate
>       allocate/deallocate memory code for all such enums using any
>       XSDE code generation options in choice_arm function

No, this is not going to be easy (unless you can change all your
types to be fixed-length). But perhaps, after reading Section 4.2,
you will see the reasoning behind doing it this way?


>   3.  What is the ideal way to create these objects for serialization

For a fixed-length choice arm you can just assing/copy by-value. For
a variable-length arm, you would allocate the arm object with new
and then pass the pointer to it. Section 4.5, "Compositors" has some
examples:

https://codesynthesis.com/projects/xsde/documentation/cxx/hybrid/guide/#4.5