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Better Codable structs with @PropertyWrappers. All credits to: http://marksands.github.io/2019/10/21/better-codable-through-property-wrappers.html
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import Foundation | |
/// Provides a default value for missing `Decodable` data. | |
/// | |
/// `DefaultCodableStrategy` provides a generic strategy type that the `DefaultCodable` property wrapper can use to provide a reasonable default value for missing Decodable data. | |
public protocol DefaultCodableStrategy { | |
associatedtype RawValue: Codable | |
static var defaultValue: RawValue { get } | |
} | |
/// Decodes values with a reasonable default value | |
/// | |
/// `@Defaultable` attempts to decode a value and falls back to a default type provided by the generic `DefaultCodableStrategy`. | |
@propertyWrapper | |
public struct DefaultCodable<Default: DefaultCodableStrategy>: Codable { | |
public var wrappedValue: Default.RawValue | |
public init(wrappedValue: Default.RawValue) { | |
self.wrappedValue = wrappedValue | |
} | |
public init(from decoder: Decoder) throws { | |
let container = try decoder.singleValueContainer() | |
self.wrappedValue = (try? container.decode(Default.RawValue.self)) ?? Default.defaultValue | |
} | |
public func encode(to encoder: Encoder) throws { | |
try wrappedValue.encode(to: encoder) | |
} | |
} | |
extension DefaultCodable: Equatable where Default.RawValue: Equatable { } | |
extension DefaultCodable: Hashable where Default.RawValue: Hashable { } | |
// MARK: - KeyedDecodingContainer | |
public extension KeyedDecodingContainer { | |
/// Default implementation of decoding a DefaultCodable | |
/// | |
/// Decodes successfully if key is available if not fallsback to the default value provided. | |
func decode<P>(_: DefaultCodable<P>.Type, forKey key: Key) throws -> DefaultCodable<P> { | |
if let value = try decodeIfPresent(DefaultCodable<P>.self, forKey: key) { | |
return value | |
} else { | |
return DefaultCodable(wrappedValue: P.defaultValue) | |
} | |
} | |
/// Default implementation of decoding a DefaultArraySorted | |
/// | |
/// Decodes successfully if key is available if not fallsback to the default value provided. | |
func decode<P>(_: DefaultArraySorted<P>.Type, forKey key: Key) throws -> DefaultArraySorted<P> { | |
if let value = try decodeIfPresent(DefaultArraySorted<P>.self, forKey: key) { | |
return value | |
} else { | |
return DefaultArraySorted(wrappedValue: []) | |
} | |
} | |
} | |
// MARK: - Default Wrappers | |
// MARK: Int | |
struct DefaultIntStrategy: DefaultCodableStrategy { | |
static var defaultValue: Int { return 0 } | |
} | |
typealias DefaultInt = DefaultCodable<DefaultIntStrategy> | |
// MARK: Double | |
struct DefaultDoubleStrategy: DefaultCodableStrategy { | |
static var defaultValue: Double { return 0.0 } | |
} | |
typealias DefaultDouble = DefaultCodable<DefaultDoubleStrategy> | |
// MARK: String | |
struct DefaultStringStrategy: DefaultCodableStrategy { | |
static var defaultValue: String { return "" } | |
} | |
typealias DefaultString = DefaultCodable<DefaultStringStrategy> | |
// MARK: Array | |
public struct DefaultEmptyArrayStrategy<T: Codable>: DefaultCodableStrategy { | |
public static var defaultValue: [T] { return [] } | |
} | |
/// Decodes Arrays returning an empty array instead of nil if appicable | |
/// | |
/// `@DefaultEmptyArray` decodes Arrays and returns an empty array instead of nil if the Decoder is unable to decode the container. | |
public typealias DefaultEmptyArray<T> = DefaultCodable<DefaultEmptyArrayStrategy<T>> where T: Codable | |
// MARK: Bool | |
struct DefaultFalseStrategy: DefaultCodableStrategy { | |
static var defaultValue: Bool { return false } | |
} | |
/// Decodes Bools defaulting to `false` if applicable | |
/// | |
/// `@DefaultFalse` decodes Bools and defaults the value to false if the Decoder is unable to decode the value. | |
typealias DefaultFalse = DefaultCodable<DefaultFalseStrategy> | |
@propertyWrapper | |
public struct DefaultArraySorted<Value: Codable & Comparable>: Codable { | |
public var wrappedValue: [Value] { | |
didSet { | |
if let comparator = comparator { | |
wrappedValue.sort(by: comparator) | |
} | |
} | |
} | |
public typealias Comparator = (Value, Value) -> Bool | |
private let comparator: Comparator? | |
public init(wrappedValue: [Value]) { | |
self.wrappedValue = wrappedValue | |
self.comparator = { $0 < $1 } | |
} | |
public init(from decoder: Decoder) throws { | |
let container = try decoder.singleValueContainer() | |
self.wrappedValue = (try? container.decode([Value].self)) ?? [Value]() | |
self.comparator = { $0 < $1 } | |
} | |
public func encode(to encoder: Encoder) throws { | |
try wrappedValue.encode(to: encoder) | |
} | |
} | |
extension DefaultArraySorted: Equatable where Value: Equatable { | |
public static func == (lhs: DefaultArraySorted<Value>, rhs: DefaultArraySorted<Value>) -> Bool { | |
return lhs.wrappedValue == rhs.wrappedValue | |
} | |
} |
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