Sketch of Recorders

recorder.cpp

template<typename D, typename T>
struct base_last_match_recorder {
  // Exploits CRTP to "up-reference" this instance from the perspective of the
  // derived class D
  void operator()(const T &v, int p) {
    if(static_cast<D*>(this)->match(v)) {
      static_cast<D*>(this)->position = p;
      static_cast<D*>(this)->value = v;
    }
  }
};

template<typename N>
struct min_recorder
  : base_last_match_recorder<min_recorder<N>, N>
{
  using numeric_type = N;

  numeric_type value;
  int position;

  constexpr min_recorder() noexcept
    : value(std::numeric_limits<numeric_type>::max())
    , position(-1)
    {}

  constexpr bool match(numeric_type n) const {
    return n < value;
  }
};

template<typename N>
struct max_recorder: base_last_match_recorder<max_recorder<N>, N> {
  using numeric_type = N;

  numeric_type value;
  int          position;

  constexpr max_recorder() noexcept
    : value(std::numeric_limits<numeric_type>::min())
    , position(-1)
    {}

  constexpr bool match(numeric_type n) const {
    return n > value;
  }
};