@safe - why does this compile?

[Timoses]

On Friday, 13 July 2018 at 11:04:40 UTC, Piotr Mitana wrote:
> This code:
>
>     import std.stdio;
>
>     class X1 {}
>     class X2 : X1
>     {
> 	void run() @safe
>         {
>             writeln("DONE");
>         }
>     }
>
>     void main() @safe
>     {
>         X1 x1 = new X1;
>         X2 x2 = cast(X2) x1;
>         x2.run();
>     }
>
> is obviously wrong gets killed by OS's signal. Why is it @safe? 
> I thought @safe should prevent such errors as well.

I suppose this is another good example of how casting can be 
dangerous?

E.g. also:

     immutable int i = 3;
     int* j = cast(int*)&i;
     assert(i == 3);
	*j = 4;
     assert(j == &i); // data occupies same address space
     assert(i == 3 && *j == 4); // yet the values differ