When and How Should You Use `enable_shared_from_this` in C ?

Understanding the Significance of enable_shared_from_this

Question:

While exploring Boost.Asio examples, many developers encounter the enable_shared_from_this concept. Despite reading the documentation, its practical application remains unclear. Could you provide an example and explain when utilizing this class is appropriate?

Answer:

enable_shared_from_this grants the ability to obtain a valid shared_ptr instance to "this," even in situations where only "this" is available. Absent this capability, obtaining a shared_ptr to "this" would necessitate having one already defined as a member.

Consider the following example from Boost's documentation:

class Y: public enable_shared_from_this<Y> {
public:
    shared_ptr<Y> f() {
        return shared_from_this();
    }
};

int main() {
    shared_ptr<Y> p(new Y);
    shared_ptr<Y> q = p->f();
    assert(p == q);
    assert(!(p < q || q < p)); // p and q must share ownership
}

The f() method returns a valid shared_ptr despite lacking a member instance.

It's important to note that simply returning a shared_ptr constructed with "this" as an argument is not an acceptable solution, as it would result in a different reference count from the legitimate "shared" one. Consequently, one of the shared pointers might end up with a dangling reference upon object deletion.

enable_shared_from_this is now part of the C 11 standard, making it accessible through both C 11 and Boost.

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