Re: proposal for new assignment operators

[Hyman Rosen <hyrosen@mail.com>]

tmoran@acm.org wrote:
>   On a recent thread we were told that the usual idiom in C++ was
> to do assignment a certain way to accomplish Finalization.  "idiom"
> suggests it's up to the programmer to do it right.  When some complex
> cases were mentioned, we were told basically that the programmer
> would override assignment differently.  Personally, I prefer having
> the computer do it, and do it right, rather than having to do it
> myself, possibly making a mistaake in the process.

You probably misunderstood what you read, then. Ada's
Controlled types don't offer anything extra over C++'s
abilities. Writing your own assignment operator in C++
is similar to writing Adjust in Ada. The constructor is
similar to Initialize, and the destructor is similar to
Finalize.

There are differences. In Ada, when a Controlled object
is initialized with an aggregate, Initialize is not called.
In C++, some constructor is always called. In Ada, assignment
is done by Finalizing the target, doing a bitwise copy of a
temporary object initialized from the source (although the
temporary mayy be elided), then calling Adjust on the target.
In C++, assignment is done by invoking the assignment operator.
The default assignment operator does elementwise assignment
for each subcomponent, but a user-written one may do whatever
it deems appropriate.