如何传递一个std :: shared_ptr但做“通过引用传递”的工作？

Question

I have a main function that takes in a reference of a class object and try to update it via foo() and bar() , however, the bar() only allows to pass into a shared_ptr type. How can I guarantee it behaves as expected, assuming I am NOT allowed to modify the signature of bar() .

void foo(MyStruct& s) {
  modifyS(s);
}

void bar(std::shared_ptr<MyStruct> s) {
  modifySAgain(s);
}

mainFunction(MyStruct& s) {
  foo(s);
  // bar(?) how should I do here such that s would be modified by bar()
  // bar(std::make_shared<Mystruct>(std::move(s)) ?
}

Answer 1

You could use a null-aliasing shared pointer:

bar(std::shared_ptr<MyStruct>(std::shared_ptr<MyStruct>(), &s));

The temporary shared pointer created in this call shares ownership with a null shared pointer, so it does nothing on destruction.

This is perhaps a bit of a hack.