Codable拡張

KeyedDecodingContainerExtension.swift

internal extension KeyedDecodingContainer {
    /// 不正なurlだとdecodeエラーになるので、nilにしてスルーする
    /// @see https://github.com/apple/swift/blob/master/stdlib/public/Darwin/Foundation/URL.swift
    /// @see https://github.com/apple/swift/blob/master/stdlib/public/core/Codable.swift.gyb
    /// @see https://github.com/apple/swift/blob/master/stdlib/public/Darwin/Foundation/JSONEncoder.swift
    func decodeIfPresent(_ type: URL.Type, forKey key: K) throws -> URL? {
        guard try contains(key) && !decodeNil(forKey: key)
            else { return nil }

        do {
            return try decode(URL.self, forKey: key)
        } catch DecodingError.dataCorrupted {
            return nil
        } catch {
            throw error
        }
    }
}