Move Constructor Syntax

[Salih Dincer]

On Tuesday, 15 October 2024 at 19:29:11 UTC, Arafel wrote:
> 
> ```d
> struct S {
> 	this (int i) { }
> 	this (S s) { }
> }
>
> void main() {
> 	S s1, s2;
> 	s1 = S(1);
> 	s2 = S(s1);
> 	// Is s1 valid here?
> }
> ```
>
> Because this is currently valid D code, even if Walter thinks 
> it shouldn't (as per the bug referenced in DIP1040 itself [3]), 
> and s1 is perfectly valid at the end of the program.

The object pointed to by s1 lives, but is destroyed if another 
object (`S(41)`) is pointed to by s1. Also, when you don't do 
`@disable this();`, objects s1 and s2 will be created twice and 
count == 3. For example:

```d
import std.stdio;

struct S
{
   int i;
   this (int i) { this.i = i; }

   S* s;
   this (ref S s) { this.s = &s; }

   @disable this();
   ~this() { ++count; }
}

int count;
enum value = 42;

void main()
{
   auto s1 = S(value);
   auto s2 = S(s1);

   s1.tupleof.writeln(": ", &s1); //42null: 7FFD6592A190
   assert(s2.s.i == value);

   s1 = S(41);

   assert(s2.s.i != value); // because value is 41
   assert(count == 1);
}
```

SDB at 79