Move Constructor Syntax

[Arafel]

On 15/10/24 11:26, Manu wrote:
> Show me a case study; what might you do with an rvalue constructor if 
> not initialise an instance from an rvalue?

I think one such case might be metaprogramming. Consider:

```d
struct S {
	int i;
	this(C)(C c) if (is(C : int)) {
		this.i = c;
	}

	alias i this;
}

void main() {
	S s1, s2, s3;
	int i = 1;
	s1 = S(1);
	s2 = S(i);
	s3 = S(s1); // This was most certainly not intended as a move constructor.
}
```

This example might seem artificial, and it is, but just imagine any 
templated constructor that uses DbI, and where the own type matches.

The actual inner details (i.e. that `S` is instantiated) might be even 
unknown to the caller, for instance if it comes from the user side of an 
API through a templated function using IFTI.

Also, you cannot use `ref` because you want it to accept both r- and 
l-values, and in any case there might be good reasons why this isn't 
desirable in metaprogramming.