On Tuesday, 20 December 2016 at 20:08:32 UTC, Ali Çehreli wrote:
If the purpose is optimization, the good news are
Yes it is :)
* Classes are already reference types so there is no lvalue or
rvalue reference distinction there
Ok, this one is quite intuitive.
import std.stdio;
...
Thank you for the illustrative example, I have reproduced it.
There is a surprising difference in D:
In D, non-constness of an object seems to be more important in
overload resolution: Notice how mutable lvalue above is passed
to by-copy instead of the potentially-more-optimal by-const-ref
above. D realizes that a mutable object is for mutation and
because by-const-ref cannot mutate it, D passes it to the
by-copy function. (This may be seen as a bug by some.)
Thank you for pointing out this. I was not aware of that, and for
sure this is not the C++ behavior.
Interestingly, enabling the by-mutable-ref overload above, now
the mutable object goes to by-ref and there is no automatic
copy:
Ok, that is "moral" and without surprise.
--- rvalue ---
constructor 1
foo(by-copy) 1
destructor for 1
--- mutable lvalue ---
constructor 2
foo(by-ref) 2
destructor for 2
--- const lvalue ---
constructor 3
foo(by-ref-const) 3
destructor for 3
Ali
[1] I have an issue with "rvalue reference" as rvalue
references can be references to lvalues as well. :p
Thank you for your time and these valuable explanations, I learnt
a lot.
--Vincent
