与预期的不同，URL即使path相同，URL也可能是不同的。因此，应避免使用init(fileURLWithPath: String, isDirectory: Bool, relativeTo: URL?)，使用appendingPathComponent(_:isDirectory:)作为替代。

let url = URL(fileURLWithPath: "foo/bar", isDirectory: false)
let baseURL = url.deletingLastPathComponent()
let newURL = URL(fileURLWithPath: "bar", isDirectory: false, relativeTo: baseURL)
let testURL = baseURL.appendingPathComponent("bar")

print(url == newURL) // prints false
print(url.path == newURL.path) // prints true

print(url == testURL) // prints true
print(url.path == testURL.path) // prints true