Stewart Gordon wrote:
Don wrote:
Andrei Alexandrescu wrote:
<snip>
Well I forgot whether BigInt is a class, is it? Anyhow, suppose it
*is* a class and as such has reference semantics. Then a += b
modifies an object in-situ, whereas a = a + b creates a whole new
object and happens to bind a to that new object.
Assuming that BigInt is mutable.
You're right, though BigInt is not a class. I have, though, seen a
BigIntRef class (in Diemos, I think) which behaved in that way. AFAIK,
the reason it existed was that the only way you can enforce value
semantics in D1 is via copy-on-write, which results in many
unnecessary heap allocations and copies.
So Fritz is correct, it could not be enforced for reference types.
The question then is, when are reference semantics desired for an
object with arithmetical operator overloading?
For matrix slices, maybe? But even then I'm not certain you'd want to
allow X=X+Y; you'd probably want to use X[]=X[]+Y[].
They would probably do different things:
Yes.
- assigning to X would reassign the reference that is X
There's no problem with X=Y. But X=X+Y would imply creating a new piece
of matrix, and assigning X to it. I'm not sure that's an operation which
you would want. I guess D strings work that way, though.
- assigning to X[] would fill X in-place.
In-place operations are straightforward: they are definitely useful.
Stewart.
