Allows more control over encoding or omitting nil values in JSON.

NilCodable.swift

/// Property wrapper that provides control over whether to explicitly encode nil values to json or not.
/// - Parameters:
///   - wrappedValue: the value to be encoded.
///   - encodeNil: Should the value be explicitly encoded as "null" in json if nil.
/// - Note:
///		Usage:
///
///		```swift
///		struct MyStruct: Codable {
///			@NilCodable var myNullable: String? // defaults to omitting null (codable default behavior)
///			@NilCodable(encodeNil: true) var myEncodedNullable: String? // Encodes "Null" in json
///			@NilCodable(encodeNil: false) var myOmittedNullable: String? // Omits Null values from json
///
///			func encode(to encoder: Encoder) throws {
///				var container = try encoder.container(keyedBy: CodingKeys.self)
///				try _myNullable.encode(to: &container, key: .myNullable)
///				try _myEncodedNullable.encode(to: &container, key: .myEncodedNullable)
///				try _myOmittedNullable.encode(to: &container, key: .myOmittedNullable)
///			}
///		}
///
///		func encodeMyStruct(myStruct: inout MyStruct, encodeNil: Bool) throws {
///			// You can set encodeNil either using projectedValue syntax, or with the provided helper method.
///			myStruct.$myNullable = encodeNil // Using property wrapper syntax
///			myStruct._myNullable.encodeNil(encodeNil) // Using the included helper method
///
///			try JSONEncoder().encode(myStruct)
///		}
///		```
@propertyWrapper public struct NilCodable<Nullable: Codable>: Codable {
	public var wrappedValue: Nullable?

	public var projectedValue: Bool {
		get { encodeNil }
		set { encodeNil = newValue }
	}

	private var encodeNil: Bool = false

	/// Property wrapper that provides control over whether to explicitly encode nil values to json or not.
	/// - Parameters:
	///   - wrappedValue: the value to be encoded.
	///   - encodeNil: Should the value be explicitly encoded as "null" in json if nil.
	/// - Note:
	///		Usage:
	///
	///		```swift
	///		struct MyStruct: Codable {
	///			@NilCodable var myNullable: String? // defaults to omitting null (codable default behavior)
	///			@NilCodable(encodeNil: true) var myEncodedNullable: String? // Encodes "Null" in json
	///			@NilCodable(encodeNil: false) var myOmittedNullable: String? // Omits Null values from json
	///
	///			func encode(to encoder: Encoder) throws {
	///				var container = try encoder.container(keyedBy: CodingKeys.self)
	///				try _myNullable.encode(to: &container, key: .myNullable)
	///				try _myEncodedNullable.encode(to: &container, key: .myEncodedNullable)
	///				try _myOmittedNullable.encode(to: &container, key: .myOmittedNullable)
	///			}
	///		}
	///
	///		func encodeMyStruct(myStruct: inout MyStruct, encodeNil: Bool) throws {
	///			// You can set encodeNil either using projectedValue syntax, or with the provided helper method.
	///			myStruct.$myNullable = encodeNil // Using property wrapper syntax
	///			myStruct._myNullable.encodeNil(encodeNil) // Using the included helper method
	///
	///			try JSONEncoder().encode(myStruct)
	///		}
	///		```
	public init(_ wrappedValue: Nullable? = nil, encodeNil: Bool = false) {
		self.wrappedValue = wrappedValue
		self.encodeNil = encodeNil
	}

	// MARK: Codable Conformance

	public init(from decoder: Decoder) throws {
		let container = try decoder.singleValueContainer()
		self.init(try container.decode(Nullable?.self))
	}

	public func encode(to encoder: Encoder) throws {
		switch wrappedValue {
		case let .some(value):
			try value.encode(to: encoder)
		case .none:
			if encodeNil {
				var container = encoder.singleValueContainer()
				try container.encodeNil()
			}
		}
	}

	/// Helper Method for setting `encodeNil`.
	/// - Note
	///		Usage:
	///			```swift
	///			_myNilCodable.encodeNil(true)
	///			```
	public mutating func encodeNil(_ encodeNil: Bool) {
		self.encodeNil = encodeNil
	}

	/// Encodes the `NilCodable` value to the provided keyed coding container.
	/// - Parameters:
	///   - container: The keyed coding container to encode to.
	///   - key: The coding key used to encode.
	/// - Throws: `EncodingError`
	public func encode<Key: CodingKey>(to container: inout KeyedEncodingContainer<Key>, key: Key) throws {
		switch (wrappedValue, encodeNil) {
		case let (.some(value), _):
			try container.encode(value, forKey: key)
		case (.none, true):
			try container.encodeNil(forKey: key)
		case (.none, false):
			try container.encodeIfPresent(wrappedValue, forKey: key)
		}
	}

	/// Encodes the `NilCodable` value to a single value container
	/// - Parameter container: the single value container to encode to.
	/// - Throws: `EncodingError`
	public func encode(to container: inout SingleValueEncodingContainer) throws {
		switch (wrappedValue, encodeNil) {
		case let (.some(value), _):
			try container.encode(value)
		case (.none, true):
			try container.encodeNil()
		case (.none, false):
			return
		}
	}
}