@protocol SDImageCache <NSObject>

This is the image cache protocol to provide custom image cache for SDWebImageManager. Though the best practice to custom image cache, is to write your own class which conform SDMemoryCache or SDDiskCache protocol for SDImageCache class (See more on SDImageCacheConfig.memoryCacheClass & SDImageCacheConfig.diskCacheClass). However, if your own cache implementation contains more advanced feature beyond SDImageCache itself, you can consider to provide this instead. For example, you can even use a cache manager like SDImageCachesManager to register multiple caches.