why doesn't C++ allow rebinding a reference?

Question

Is it a problem to rebind a reference? I've searched this question on Google, but I can't find relevant answers to this question. What made the designers of C++ decided to make it that way?

Answer 1

Stroustrup's The Design & Evolution of C++ answers most questions of this kind. In this case, see the section §3.7 References:

I had in the past been bitten by Algol68 references where r1=r2 can either assign through r1 to the object referred to or assign a new reference value to r1 (re-binding r1) depending on the type of r2. I wanted to avoid such problems in C++.
If you want to do more complicated pointer manipulation in C++, you can use pointers.

Answer 2

References are useful because they don't support unsafe pointer arithmetic and will never be null. On the other hand, pointers can be rebound and can be placed in STL containers. A trade off with all these useful properties is std::reference_wrapper:

#include <functional>
#include <iostream>
#include <string>

int main() {
  std::string s1 = "my", s2 = "strings";

  auto r = std::ref(s1);  // bind

  // use r.get() to access the referenced object
  std::cout << '\'' << r.get() << "' has " << r.get().size() << " characters\n";

  r = s2;  // rebind

  // use the other object
  std::cout << '\'' << r.get() << "' has " << r.get().size() << " characters\n";
}