A simple statically allocated cache, auto-clears on overflow

static_cache.hpp

template <typename ValT, std::size_t Capacity>
class StaticCache {
 public:
  ValT &operator[](std::uint32_t hash) {
    for (std::size_t i = 0; i < num_entries; ++i) {
      if (entries[i].hash == hash) return entries[i].value;
    }

    if (++num_entries > Capacity) num_entries = 1;

    auto &entry = entries[num_entries - 1];
    entry.hash = hash;
    entry.value = ValT{};
    return entry.value;
  }

  void clear() { num_entries = 0; }

 private:
  struct Entry {
    std::uint32_t hash;
    ValT value;
  };

  Entry entries[Capacity];
  std::size_t num_entries{};
};