Return a reference problem

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C++

Hi I have a problem (maybe it is not a difficult problem but I am stuck for about 2 days) that is to return a reference to a string in a variadic template. To show my problem, I will omit the variadic template part (the problem still the same and it is for me easier to explain).

So, the situation is the follows:

class A
{
public:
  A() {}
  ~A(){}
  std::string str;

  std::string& get_str() {return str;};
};

void wmain( int argc, char** args)
{
  A a;
  a.get_str() = "hello world";
  // now a.str value is 'hello world', works as expected
}

Now I will add a function in the middle of the process:

class A
{
public:
  A() {}
  ~A(){}
  std::string str;

  std::string& get_str() {return str;};
};

std::string& bridge(A a)
{
  return a.get_str();
}

void wmain( int argc, char** args)
{
  A a;
  bridge(a) = "hello world"; // a little error :D
}

So, how I must design the bridge function to achieve the same behavior as in the first case?

Best regards
Filipe Marques