Return `std::shared_ptr` by reference

Question

I am reading some codebase but I don't quite understand why the below function would return a reference (&) to the std::shared_ptr. I read in this stackoverflow question that we should return std::shared_ptr by value, because otherwise we won't properly increment the reference count.

So I am just trying to guess the reason.

Does it have something to do with the the member function being static? Or the return value being static?
Does it have something to do with thread as the name suggests? Could anyone point me to some reading or give some direction?

class A {
    public:
        A() {...}
        ~A() {...}
        ...
        static std::shared_ptr<A>& ThreadLocal() {
            static std::shared_ptr<A> inst = std::make_shared<A>();
            if (inst == nullptr) {
                inst = std::make_shared<A>();
            }
            return inst;
        }
        static void Shutdown() {
            ThreadLocal().reset();
        }
    private:
        ...
}

`ThreadLocal` using `static` rather than `thread_local`? What the deuce? — Bathsheba, Jan 19 '19 at 19:33
`static` in a declaration always apply to the name being declared. — curiousguy, Jan 19 '19 at 22:06

score 2 · Accepted Answer · answered Jan 19 '19 at 19:15

2

One of the reasons it's returned by reference is to reset the static shared pointer. You can see that there is some logic to create a new one for whatever business logic the static pointer could need to be reset.

And no, no logic for threads here.

answered Jan 19 '19 at 19:15

Matthieu Brucher

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Hmm great point! I also question myself why would one want to check that line: `if (inst == nullptr)`. – IgNite Jan 19 '19 at 19:22
I'd like to spend some time a bit more diving into the code to see exactly why. But your answer gives me a really good direction of where to look into. – IgNite Jan 19 '19 at 19:29

Return `std::shared_ptr` by reference

1 Answers1