How to Replace Default Deletion with Custom Destructors for Boost\'s Shared Pointers?

Replacing Default Deletion with Custom Destructors for Shared Pointers

Boost's shared_ptr typically employs the delete function to destruct its allocated objects. However, there are scenarios where developers may want to utilize custom destructors.

Overriding Default Deletion

To override the default deletion behavior, you can use a member function as the custom destructor. For example:

<code class="cpp">class CustomDeletable {
public:
    void deleteMe() {
        // Implement custom deletion logic here
    }
};

boost::shared_ptr<CustomDeletable> ptr(new CustomDeletable, &CustomDeletable::deleteMe);</code>

Handling C-Style Functions

For C-style functions that return pointers, you can employ a wrapper functor to redirect the deletion process:

<code class="cpp">// Custom destructor functor for C-style functions
struct LibFreeFunctor {
    void operator()(void *ptr) {
        lib_freeXYZ(ptr);
    }
};

// Usage with shared_ptr
boost::shared_ptr<void> ptr(new void*, LibFreeFunctor());</code>

Using the STL's Wrapper Functors

Alternatively, STL provides wrapper functors that can be used without requiring a custom caller:

<code class="cpp">boost::shared_ptr<T> ptr(new T, std::mem_fun_ref(&T::deleteMe));
boost::shared_ptr<S> ptr(new S, std::ptr_fun(lib_freeXYZ));</code>

By utilizing these techniques, you can tailor shared_ptr to call custom destructors, providing flexibility in managing object lifetimes and resource deallocation.

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