callback.h

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#pragma once
 
#include "fl/namespace.h"
 
namespace fl {

template<typename ...Args>
class Callback {
public:
    Callback() = default;
    // Member function constructor.
    Callback(void* self, void (*callback)(void* self, Args... args)) : self(self), callback(callback) {}
    // Free function constructor.
    explicit Callback(void* (*callback)(Args... args)) : self(nullptr), callback((void (*)(void*, Args...))callback) {}
    Callback(const Callback&) = default;
    operator bool() const { return callback != nullptr; }
    void operator()(Args... args) const { if (callback) callback(self, args...); }
    void clear() { callback = nullptr; self = nullptr; }
    bool operator==(const Callback& other) const { return self == other.self && callback == other.callback; }
    bool operator!=(const Callback& other) const { return !(*this == other); }
    Callback& operator=(const Callback& other) { self = other.self; callback = other.callback; return *this; }
    Callback& operator=(void* (*other)(Args... args)) { self = nullptr; callback = (void (*)(void*, Args...))other; return *this; }
    Callback& operator=(void (*other)(void* self, Args... args)) { self = nullptr; callback = other; return *this; }
    // operator < for set/map
    bool operator<(const Callback& other) const { return self < other.self || (self == other.self && callback < other.callback); }
private:
    void* self = nullptr;
    void (*callback)(void* self, Args... args) = nullptr;
};
 
}  // namespace fl