On Efficient Concurrency, Sharing, Move Semantics in Rust vs D

[via Digitalmars-d]

On Tuesday, 13 May 2014 at 11:04:18 UTC, Nordlöw wrote:
>>> but I believe it would be better to let the (D) compiler 
>>> optimization stage figure out _automatically_ if it needs to 
>>> make a copy of the variable `numbers` or not depending on 
>>> whether `numbers` is used or not further down the body of
>
> I'm surprised that nobody has answered this discussion...
>
> Isn't this an important question/possibility now that we soon 
> have inference of uniqueness/immutability in DMD from Walters 
> work?
>
> Ping!

In general, anything that involves optimization must by 
definition not change program behavior. Copying vs. not copying 
usually has visible consequences, and therefore cannot be decided 
by the optimizer.

Furthermore, I think it is too fragile to (silently) base a 
decision about copying on what happens further down the program. 
You could too easily change something by accident.

The uniqueness changes in DMD are different, although I believe 
they are not yet properly documented. Uniqueness is only decided 
from the the expression that produced the value, but not from 
what further happens with the value.