Overwriting an object with an object of same type

Question

Is the following well defined?

#include 
#include 

using namespace std;

struct Const {
    const int i; 
    Const (int i)          


        

Answer 1

This is only intended as an addendum to @Tony D's answer, regarding

new (p) Const(2) erase the old object stored at p

I think you need to differentiate between an object and the conceptual idea of an "instance".

[...] An object is a region of storage.[...]

[N4431 §1.8/1]

So the pointer p points to a region of storage, which contains the bit pattern of some "instance" before the placement new and some different bit pattern of a different, but well constructed "instance" of the correct (same) type.

So at the location pointed to by p there's a valid object, and when assigning q from it q points to it. Though as noted in the other answer, accessing it via p isn't permited.