How can I make my class immune to the “auto value = copy of proxy” landmine in C++?

Reduce the damage by adding “&&” to the end of the proxy class’s operator=

(And operator +=, -=, etc.)

Took me a lot of experimenting but I eventually found a way to mitigate the most common case of the problem, this tightens it so you can still copy the proxy, but once you’ve copied it to a stack variable, you can’t modify it and inadvertently corrupt the source container.

#include <cstdio>
#include <utility>

auto someComplexMethod()
{
  struct s
  {
    void operator=(int A)&& {std::printf("Setting A to %i", A);}
  };
  return s();
}

int main()
{
  someComplexMethod() = 4; // Compiles. Yay

  auto b = someComplexMethod(); 
  // Unfortunately that still compiles, and it's still taking a 
  // copy of the proxy, but no damage is done yet.

  b = 5; 
  // That doesn't compile. Error given is: 
  //   No overload for '='  note: candidate function not viable: 
  //   expects an rvalue for object argument

  std::move(b) = 6; 
  // That compiles, but is basically casting around the 
  // protections, aka shooting yourself in the foot.
}