Re: Constructors/Destructors in Ada95

[Francois Godme <fgodme@bigfoot.com>]

I would like to add some other arguments not yet expressed:

   * against the non-primitive procedures used as constructors of limited
     instances like in Tucker Taft's proposal,
   * against the Adjust procedure and
   * against the Finalize procedure.

I. Non-primitive procedures used as constructors of limited instances:
As limited instances can't be initialized with record aggregates, it is
possible to write code which forgets to initialize all record fields. It was
already the case in Ada83 but only in the horizontal plane. With procedures, it
can now get wrong in the vertical plane along the class hierarchy if one forgot
to call one of the initializing procedures of its immediate super-class.
Programmers have also to remember to call the super-class procedure first as a
precaution before initializing extension record fields. Nothing insurmountable
I admit. If the language had constructors, the compiler could warn me when I
forgot something in the horizontal or the vertical plane. This will increase
safety.

This doesn't apply to non-limited types if they are initialized only with
aggregates and functions. No procedures.

II.The Adjust procedure:
Efficiency concerns may be raised against the sequence: Finalize (Target);
shallow copy Source into Target; Adjust (Target);.

In the Adjust procedure, control is given to perform, for instance, a deep copy
of Source into Target. One can easily devise situations where Finalize of
Target will have to deallocate memory which will be immediately needed and
reallocated by Adjust of Target.

III. The Finalize procedure:
The programmers are responsible in the Finalize procedure to call last the
immediate super-class Finalize procedure. As the notion of immediate
super-class does not exist in the language, it is not possible to write code
that will always call the Finalize procedure of the immediate super-class.