callback.hpp

/*
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#ifndef OTBR_COMMON_CALLBACK_HPP_
#define OTBR_COMMON_CALLBACK_HPP_
 
#include <functional>
#include <type_traits>
 
namespace otbr {
 
template <class T> class OnceCallback;
 
template <typename R, typename... Args> class OnceCallback<R(Args...)>
{
public:
    // Constructs a new `OnceCallback` instance with a callable.
    //
    // This constructor is for matching std::function<> and lambda and the
    // `std::enable_if_t` check is only required for working around gcc 4.x
    // compiling issue which trying to instantiate this template constructor
    // for use cases like `::mOnceCallback(aOnceCallback)`.
    template <typename T, typename = typename std::enable_if<!std::is_same<OnceCallback, T>::value>::type>
    OnceCallback(T &&func)
        : mFunc(std::forward<T>(func))
    {
    }
 
    OnceCallback(const OnceCallback &) = delete;
    OnceCallback &operator=(const OnceCallback &) = delete;
    OnceCallback(OnceCallback &&)                 = default;
    OnceCallback &operator=(OnceCallback &&) = default;
 
    R operator()(Args...) const &
    {
        static_assert(!sizeof(*this), "OnceCallback::() can only be invoked on a non-const "
                                      "rvalue, i.e. std::move(callback)().");
    }
 
    R operator()(Args... args) &&
    {
        // Move `this` to a local variable to clear internal state
        // before invoking the callback function.
        OnceCallback cb = std::move(*this);
 
        return cb.mFunc(std::forward<Args>(args)...);
    }
 
    bool IsNull() const { return mFunc == nullptr; }
 
private:
    std::function<R(Args...)> mFunc;
};
 
} // namespace otbr
 
#endif // OTBR_COMMON_CALLBACK_HPP_