How to get an element based on raw_ptr from an unordered_set keyed on shared_ptr

Question

I am wondering if there is anyway for me to retrieve an element based on its raw pointer from an unordered_set keyed on shared_ptr.

unordered_set< shared_ptr<MyObj> > sets;
auto myobj = make_shared<MyObj>();
sets.insert(myobj);

// Find the element myobj
sets.find(myobj);

// How to find the element based on the underlying raw pointer?
sets.find(my.obj.get()); <---- apparently this gives compile error

// This method works but it will double free myobj though (not correct)
sets.find(shared_ptr<MyObj>(my.obj.get()));

Answer 1

You can declare MyObj as:

class MyObj : public std::enable_shared_from_this<MyObj>
{
     ....
}

This adds a method returning a shared pointer for a given object instance.

MyObj * rawptr = myobj.get();
sets.find(rawptr->shared_from_this());

Note that prior to calling shared_from_this() on an object, there must be a std::shared_ptr that owns it.