Containers

[vit]

On Tuesday, 31 August 2021 at 17:21:02 UTC, deadalnix wrote:
> ...
> For instance, if we have a Vector!T, then we want it to convert 
> to a Vector!(const T) and we want const(Vector!T) == 
> const(Vector!(const T)), all of it implicitly. Same goes for 
> other qualifiers.
>
> To put it bluntly, I have no idea how to achieve this. And I 
> don't think we'll have a good set of collection before this is 
> sorted out.
> ...

Try `this` template parameter:

```d
import std.traits : CopyConstness, isMutable;


void main(){
     {
         Vector!int a;
         Vector!(const int) b = a;
         const Vector!int c = b;
     }
     {
         Vector!int a;
         Vector!(const int) b;
         b = a;
     	
     }
}


struct Vector(T){
     alias ElementType = T;

     this(U, this This)(ref Vector!U rhs)
     if(!is(U == T) && isCopyable!(This, typeof(rhs))){
     	//impl
     }

     this(U, this This)(Vector!U rhs)
     if(isCopyable!(typeof(rhs), This)){
     	//impl
     }

	///TODO copy ctors...

     void opAssign(U, this This)(auto ref Vector!U rhs)
     if(isCopyable!(typeof(rhs), This) && isMutable!This){
     	//impl
     }
}

private enum bool isCopyable(From, To) = is(
	CopyConstness!(From, From.ElementType[]) : CopyConstness!(To, 
To.ElementType[])
);

```