If I do:
```d
struct S1
{
const int* my_x;
this(const int* x) { my_x = x; }
}
struct S2
{
int* my_x;
this(int* x) { my_x = x; }
}
main()
{
immutable int i = 5;
S1 s = S1(&i); // works
immutable S2 t = S2(&i); // fails
}
```
Shoudn't S2 also work? It's immutable, so even if it takes only a
mutable parameter, it is ensured it will not change it, because
it is itself immutable, so none of its attributes can be modified
nor can non-const member functions be called.
Is there a deeper reason why this is not allowed? Or is it simply
not implemented?
