Comment by UncleMeat

???

You can absolutely write a type like this.

    class Foo {
     public:
      Foo() {}  // never initialized x
      int x; 
    }

And then using it like this

    Foo f;
    bar(foo.x);  // oops

"But my types are well designed" is the usual response to "why the heck does the language allow you to quietly expose yourself to UB in this way?"