why diskConfig.cachePathBlock should be reset to nil here? - swift

Question

I'm watching the source code of Kingfisher. And i have an question in the following code (Source code):
why reset diskConfig.cachePathBlock to nil at the end of init method?
I can't figure it out.
public convenience init(
name: String,
cacheDirectoryURL: URL?,
diskCachePathClosure: DiskCachePathClosure? = nil) throws
{
if name.isEmpty {
fatalError("[Kingfisher] You should specify a name for the cache. A cache with empty name is not permitted.")
}
let totalMemory = ProcessInfo.processInfo.physicalMemory
let costLimit = totalMemory / 4
let memoryStorage = MemoryStorage.Backend<Image>(config:
.init(totalCostLimit: (costLimit > Int.max) ? Int.max : Int(costLimit)))
var diskConfig = DiskStorage.Config(
name: name,
sizeLimit: 0,
directory: cacheDirectoryURL
)
if let closure = diskCachePathClosure {
diskConfig.cachePathBlock = closure
}
let diskStorage = try DiskStorage.Backend<Data>(config: diskConfig)
diskConfig.cachePathBlock = nil
self.init(memoryStorage: memoryStorage, diskStorage: diskStorage)
}

Answer 1

Not setting the property to nil would keep a strong reference to the passed-in closure and potentially create a memory leak. Setting it to nil avoids this.
Assuming the nil assignment were not present, here's an example for a leak:
class CacheBuilder {
func createCache() -> ImageCache {
let cache = try! ImageCache(name: "Cache", cacheDirectoryURL: nil, diskCachePathClosure: self.path)
return cache
}
func path(_ url: URL, _ str: String) -> URL {
return url
}
deinit {
print("deinit") // is not called when Cache.init is done
}
}
class Cache {
let cache: ImageCache
init() {
let builder = CacheBuilder()
self.cache = builder.createCache()
}
}