What should delegates with qualifiers mean?

[Paul Backus]

On Wednesday, 24 March 2021 at 19:23:15 UTC, Q. Schroll wrote:
> While everywhere else, immutable is a requirement and a 
> guarantee, here it is a guarantee only. That is because the 
> context object cannot be reassigned independently of the 
> function pointer. Therefore, a `delegate() immutable` is 
> convertible to a `delegate() const` delegate which in turn is 
> convertible to a `delegate()`.

No, this is unsound, because a delegate may return a pointer or 
reference to its context. Consider:

struct S
{
     int n;
     int* getPtr() { return &n; }
}

void main() @safe
{
     immutable S s = { 123 };
     // implicitly convert from `delegate() immutable` to 
`delegate()`
     int* delegate() dg = &s.getPtr;
     // undefined behavior
     *dg() = 456;
}