LenientDecode.swift

extension KeyedDecodingContainer {
    func lenientDecode<T>(_ type: T.Type, forKey key: KeyedDecodingContainer.Key) throws -> T where T: Decodable & LosslessStringConvertible {
        do {
            return try decode(T.self, forKey: key)
        } catch {
            guard let stringValue = try? decode(String.self, forKey: key), let t = T(stringValue) else { throw error }
            return t
        }
    }
}

struct Stop: Codable {
    let id: Int
    let name: String
    let x, y: Int?      // sometimes wrongly encoded as a string "12345"

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        id = try values.lenientDecode(Int.self, forKey: .id)
        name = try values.decode(String.self, forKey: .name)
        x = try values.lenientDecode(Int.self, forKey: .x)
        y = try values.lenientDecode(Int.self, forKey: .y)
    }
}

For those times when an API throws randomly quoted numbers at you.