Safe Decode

decodeSafelyIfPresent.swift

public protocol DefaultValueProviding {
    static var defaultValue: Self { get }
}

extension String: DefaultValueProviding {
    public static var defaultValue: String  { return "" }
}

extension Int: DefaultValueProviding {
    public static var defaultValue: Int  { return 0 }
}

extension KeyedDecodingContainer {

    /// It works the same as the foundation `decodeIfPresent` but infers the type of
    /// value to decode from the context.
    public func decodeIfPresent<T: Decodable>(forkey key: Key) throws -> T? {
        return try decodeIfPresent(T.self, forKey: key)
    }

    /// Decodes a value of the inferred type, or returns the default value if the value
    /// is a null value, or if there are no more elements to decode, or if the type of
    /// the element doesn't match the inferred type.
    public func decodeSafelyIfPresent<T: Decodable>(forKey key: Key, defaultValue: T) -> T {
        do {
            return try decodeIfPresent(T.self, forKey: key) ?? defaultValue
        } catch {
            return defaultValue
        }
    }

    /// Decodes a value of the inferred type, or returns the default value provided
    /// using `DefaultValueProviding` protocol if the value is a null value,
    /// or if there are no more elements to decode, or if the type of the element
    /// doesn't match the inferred type.
    public func decodeSafelyIfPresent<T: Decodable & DefaultValueProviding>(forKey key: Key) -> T {
        return decodeSafelyIfPresent(forKey: key, defaultValue: T.defaultValue)
    }
}