C++ High Performance

Example 3 – Hash strings at compile time

Let's say you have a resource system consisting of an unordered map of strings which identify bitmaps. If the bitmap is already loaded, it returns the loaded bitmap; otherwise it loads the bitmap and returns it.

// External function which loads a bitmap from the filesystemauto load_bitmap_from_filesystem(const char* path) -> Bitmap {...} 
 
// Bitmap cache 
auto get_bitmap_resource(const std::string& path) -> const Bitmap& { 
  // Static storage of all loaded bitmaps 
  static auto loaded = std::unordered_map<std::string, Bitmap>{}; 
  // If the bitmap is already in loaded_bitmaps, return it 
  if (loaded.count(path) > 0) { 
    return loaded.at(path); 
  } 
  // The bitmap isn't already loaded, load and return it 
  auto bitmap ...