What ever happened to move semantics?

[Dukc]

On Thursday, 29 February 2024 at 04:17:38 UTC, Walter Bright 
wrote:
> DFA works with mathematical reliability (absent compiler bugs). 
> The optimizer relies heavily on DFA; if DFA was unreliable the 
> whole edifice will fall apart. Leave move vs copy to the 
> compiler. The move vs copy/destroy choice is an optimization, 
> and should be semantically thought of it that way.

I'm a bit worried this would lead to implementation-defined 
behaviour on whether uses of a struct with a disabled copy 
constructor would compile.

But otherwise I agree with this. Well, the spec currently doesn't 
allow these elision in all cases, for example it says:

```D
struct A
{
     this(ref return scope A another) {}
}

void fun(A a) {}

void main()
{
     A a;
     fun(a);    // copy constructor gets called
}
```

...but I tend to agree it should be implementation-defined 
whether the copy constructor is called here.