value_tracker.hpp

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#ifndef EAGINE_VALUE_TRACKER_HPP
#define EAGINE_VALUE_TRACKER_HPP
 
#include <type_traits>
 
namespace eagine {
//------------------------------------------------------------------------------
template <typename T, typename Transform>
class value_change_tracker : Transform {
    static_assert(std::is_arithmetic_v<T>);
 
public:
    value_change_tracker() noexcept = default;
 
    value_change_tracker(T initial) noexcept
      : _prev{std::move(initial)} {}
 
    value_change_tracker(T initial, Transform transf) noexcept
      : Transform(std::move(transf))
      , _prev{std::move(initial)} {}
 
    auto transform(const T& value) noexcept {
        return _transform()(value);
    }
 
    auto get() const noexcept -> const T& {
        return _prev;
    }
 
    auto has_changed(const T& next) noexcept -> bool {
        if(transform(_prev) != transform(next)) {
            _prev = next;
            return true;
        }
        return false;
    }
 
private:
    auto _transform() noexcept -> Transform& {
        return *this;
    }
 
    T _prev{0};
};
//------------------------------------------------------------------------------
template <typename T, T D>
struct value_change_divider {
    auto operator()(const T& value) noexcept -> T {
        return T(value / D);
    }
};
//------------------------------------------------------------------------------
template <typename T, T D>
using value_change_div_tracker =
  value_change_tracker<T, value_change_divider<T, D>>;
//------------------------------------------------------------------------------
} // namespace eagine
 
#endif // EAGINE_VALUE_TRACKER_HPP