Discussion: Rvalue refs and a Move construtor for D

[kinke]

On Thursday, 29 August 2019 at 08:58:55 UTC, RazvanN wrote:
> https://github.com/RazvanN7/DIPs/blob/Move_Constructor/DIPs/DIP1xxx-rn.md

> Currently, the DMD compiler does not perform any move operations

It does, the classical example being passing an rvalue argument 
by value to the callee:

struct S
{
     long[32] data;
     this(this) {}
     ~this() {}
}

void callee(S s) {}

void caller() { callee(S()); }

It allocates a first S instance on the caller stack and then 
moves that into a 2nd instance on the callee params stack 
(current D ABI on Posix x86_64 - non-PODs passed by value are 
passed on the stack), blitting the 32*8 bytes but eliding 
postblit (and destruction of the 1st instance) and letting callee 
destruct the moved-into 2nd instance.
C++ passes a ref under the hood in such a case and can thus 
simply pass a pointer to the first instance, no blitting 
happening at all.