Gc/D_runtime prevents dangling pointers?

[tipdbmp]

char * get_dangling_ptr() {
     char[] a;
     a.reserve(15);

     a ~= 'x';
     char *x = &a[0];

     auto a_initial_ptr = a.ptr;
     foreach (_; 0 .. 30) {
         a ~= 'y';
         //a.assumeSafeAppend() ~= 'y';
     }
     assert(a.ptr != a_initial_ptr, "a should've reallocated");

      // trying to reuse 'a's old memory
     foreach (_; 0 .. 10) {
         char[] b;
         b.reserve(15);
         foreach (__; 0 .. 15) {
             b ~= 'y';
         }
     }

     return x;
}

void main() {
     import std.stdio : writefln;
     char *x = get_dangling_ptr();
     writefln("ptr: %X; value: %s", x, *x);
}

x doesn't seem to be a dangling pointer, how come?