How Does `enable_shared_from_this` Solve Shared Pointer Ownership Issues in C ?

How Does enable_shared_from_this Help in Maintaining Object Ownership?

While exploring Boost.Asio examples, you may have encountered enable_shared_from_this. Despite referencing the documentation, its usage remains unclear. Here's a comprehensive explanation and an example to clarify its purpose.

enable_shared_from_this allows you to create a valid shared_ptr instance for the object when you only have access to the object itself (represented by this). Without it, obtaining a shared_ptr for this would be impossible unless it was already defined as a member.

Consider the following example:

class Y: public enable_shared_from_this<Y>
{
public:

    shared_ptr<Y> f()
    {
        return shared_from_this();
    }
};

Here, method f() can return a valid shared_ptr, even though it lacks a member instance. Note that the following approach would fail:

class Y: public enable_shared_from_this<Y>
{
public:

    shared_ptr<Y> f()
    {
        return shared_ptr<Y>(this);
    }
};

The result would be two shared_ptrs with different reference counts. When the object is deleted, one of them will become a dangling reference.

It's important to note that enable_shared_from_this is now part of the C 11 standard, making it accessible from there as well as from Boost.

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