Return type deduction in recursive function

Question

Following code compiles :

auto foo(int i) {
  if( i == 1 )
    return i;
  else 
    return foo(i-1)+i ; 
}

While following doesn\'t,

Answer 1

A recursive function can have an auto return type only if it has a non-recursive return statement before the recursive call. See Return type deduction for normal functions.