How Can We Implement an Autonomous `self` Member Type in C ?

Implementing an Autonomous self Member Type in C

PHP supports the self keyword within a class, which evaluates to the class's type. C , however, lacks an equivalent.

To simulate this behavior per class, one can use a simple typedef:

struct Foo
{
   typedef Foo self;
};

While this works, it requires explicitly specifying the class name, increasing the risk of silent errors.

To achieve autonomous self member typing, we can leverage decltype and friends:

template <typename... Ts>
class Self;

template <typename X, typename... Ts>
class Self<X, Ts...> : public Ts...
{
protected:
    typedef X self;
};

#define WITH_SELF(X) X: public Self<X>
#define WITH_SELF_DERIVED(X, ...) X: public Self<X, __VA_ARGS__>

By using these macros, you can effortlessly implement self member typing:

class WITH_SELF(Foo)
{
    void test()
    {
        self foo;
    }
};

For derived classes, employ WITH_SELF_DERIVED:

class WITH_SELF_DERIVED(Bar, Foo)
{
    /* ... */
};

This approach not only eliminates the need to explicitly specify class names but also supports multiple inheritance.

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