> Intuitively, example 2 looks like it should be undefined but I can't
 > find any wording that says so.

This was a defect in the standard, you'll be interested to read:

   http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#89

~Marc.

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// example 1
struct foo {
 const int a;
 foo(int a) : a(a) {}
 foo & operator=(const foo &f)
 {
  if (&f != this) {
   this->~foo();
   new (this) foo(f);
// undefined by 3.8/9
  }
  return *this;
 }
};

foo f(3);
f = foo(4);
cout << f.a;


// example 2
struct foo {
 int &a;
 foo(int &a) : a(a) {}
 foo & operator=(const foo &f)
 {
  if (&f != this) {
   this->~foo();
   new (this) foo(f);
// undefined?
  }
  return *this;
 }
};

int a = 3, b = 4;
foo f(a);
f = foo(b);
cout << f.a;

Intuitively, example 2 looks like it should be undefined but I can't
find any wording that says so.

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