feat(HelperCoders): added conditional and property wrapper based helpers

Author: soumyamahunt

Sources/HelperCoders/ConditionalCoder.swift

@@ -0,0 +1,78 @@
+import MetaCodable
+
+/// An ``/MetaCodable/HelperCoder`` that helps decoding/encoding
+/// with two separate ``/MetaCodable/HelperCoder``s.
+///
+/// This type can be used to use separate ``/MetaCodable/HelperCoder``s
+/// for decoding and encoding.
+public struct ConditionalCoder<D: HelperCoder, E: HelperCoder>: HelperCoder
+where D.Coded == E.Coded {
+    /// The ``/MetaCodable/HelperCoder`` used for decoding.
+    @usableFromInline
+    internal let decoder: D
+    /// The ``/MetaCodable/HelperCoder`` used for encoding.
+    @usableFromInline
+    internal let encoder: E
+
+    /// Creates a new instance of ``/MetaCodable/HelperCoder`` that decodes/encodes
+    /// conditionally with provided decoder/encoder respectively.
+    ///
+    /// The provided decoder is used only for decoding
+    /// and encoder only for encoding.
+    ///
+    /// - Parameters:
+    ///   - decoder: The ``/MetaCodable/HelperCoder`` used for decoding.
+    ///   - encoder: The ``/MetaCodable/HelperCoder`` used for encoding.
+    public init(decoder: D, encoder: E) {
+        self.decoder = decoder
+        self.encoder = encoder
+    }
+
+    /// Decodes using the decode specific ``/MetaCodable/HelperCoder``
+    /// from the given `decoder`.
+    ///
+    /// - Parameter decoder: The decoder to read data from.
+    /// - Returns: The decoded value.
+    /// - Throws: If the underlying ``/MetaCodable/HelperCoder`` throws error.
+    @inlinable
+    public func decode(from decoder: Decoder) throws -> D.Coded {
+        return try self.decoder.decode(from: decoder)
+    }
+
+    /// Decodes optional value using the decode specific
+    /// ``/MetaCodable/HelperCoder`` from the given `decoder`.
+    ///
+    /// - Parameter decoder: The decoder to read data from.
+    /// - Returns: The decoded optional value.
+    /// - Throws: If the underlying ``/MetaCodable/HelperCoder`` throws error.
+    @inlinable
+    public func decodeIfPresent(from decoder: Decoder) throws -> D.Coded? {
+        return try self.decoder.decodeIfPresent(from: decoder)
+    }
+
+    /// Encodes using the encode specific ``/MetaCodable/HelperCoder``
+    /// from the given `encoder`.
+    ///
+    /// - Parameters:
+    ///   - value: The value to encode.
+    ///   - encoder: The encoder to write data to.
+    ///
+    /// - Throws: If the underlying ``/MetaCodable/HelperCoder`` throws error.
+    @inlinable
+    public func encode(_ value: E.Coded, to encoder: Encoder) throws {
+        try self.encoder.encode(value, to: encoder)
+    }
+
+    /// Encodes optional value using the encode specific
+    /// ``/MetaCodable/HelperCoder`` from the given `encoder`.
+    ///
+    /// - Parameters:
+    ///   - value: The value to encode.
+    ///   - encoder: The encoder to write data to.
+    ///
+    /// - Throws: If the underlying ``/MetaCodable/HelperCoder`` throws error.
+    @inlinable
+    public func encodeIfPresent(_ value: E.Coded?, to encoder: Encoder) throws {
+        try self.encoder.encodeIfPresent(value, to: encoder)
+    }
+}

Sources/HelperCoders/HelperCoders.docc/HelperCoders.md

@@ -14,6 +14,8 @@ Level up ``/MetaCodable``'s generated implementations with helpers assisting com
 - Custom `Date` decoding/encoding approach, i.e. converting from UNIX timestamp, text formatted date etc.
 - Custom `Data` decoding/encoding approach, i.e. converting from base64 text etc.
 - Decoding/encoding non-confirming floats with text based infinity and not-a-number representations.
+- Conditionally decode/encode with two helpers each handling one.
+- Using existing property wrappers for custom decoding/encoding.
 
 ## Installation
 
@@ -54,3 +56,9 @@ Level up ``/MetaCodable``'s generated implementations with helpers assisting com
 ### Data
 
 - ``Base64Coder``
+
+### Composition
+
+- ``PropertyWrapperCoder``
+- ``PropertyWrappable``
+- ``ConditionalCoder``

Sources/HelperCoders/PropertyWrapperCoder.swift

@@ -0,0 +1,56 @@
+import MetaCodable
+
+/// An ``/MetaCodable/HelperCoder`` that helps decoding/encoding
+/// using existing property wrappers.
+///
+/// This type can be used to reuse existing property
+/// wrappers with custom decoding/encoding with
+/// ``MetaCodable`` generated implementations.
+public struct PropertyWrapperCoder<Wrapper: PropertyWrappable>: HelperCoder {
+    /// Creates a new instance of ``/MetaCodable/HelperCoder`` that decodes/encodes
+    /// using existing property wrappers.
+    ///
+    /// - Returns: A new property wrapper based decoder/encoder.
+    public init() {}
+
+    /// Decodes using `Wrapper` type from the given `decoder`.
+    ///
+    /// - Parameter decoder: The decoder to read data from.
+    /// - Returns: The wrapped value decoded.
+    /// - Throws: If the property wrapper throws error.
+    @inlinable
+    public func decode(from decoder: Decoder) throws -> Wrapper.Wrapped {
+        return try Wrapper(from: decoder).wrappedValue
+    }
+
+    /// Encodes given value using `Wrapper` type to the provided `encoder`.
+    ///
+    /// - Parameters:
+    ///   - value: The wrapped value to encode.
+    ///   - encoder: The encoder to write data to.
+    ///
+    /// - Throws: If the property wrapper throws error.
+    @inlinable
+    public func encode(_ value: Wrapper.Wrapped, to encoder: Encoder) throws {
+        try Wrapper(wrappedValue: value).encode(to: encoder)
+    }
+}
+
+/// A type representing a [property wrapper].
+///
+/// A property wrapper adds a layer of separation
+/// between code that manages how a property is stored
+/// and the code that defines a property.
+///
+/// [property wrapper]: https://docs.swift.org/swift-book/documentation/the-swift-programming-language/properties/#Property-Wrappers
+public protocol PropertyWrappable: Codable {
+    /// The type of the value wrapped.
+    associatedtype Wrapped
+    /// The value wrapped.
+    var wrappedValue: Wrapped { get }
+    /// Creates new instance wrapping provided value.
+    ///
+    /// - Parameters:
+    ///   - wrappedValue: The value to be wrapped.
+    init(wrappedValue: Wrapped)
+}

Tests/MetaCodableTests/HelperCoders/HelperCodersTests.swift

@@ -0,0 +1,78 @@
+import HelperCoders
+import MetaCodable
+import XCTest
+
+final class HelperCodersTests: XCTestCase {
+    func testConditionalCoding() throws {
+        let jsonStr = """
+            {
+                "date": "1997-11-04T10:38:21Z",
+                "optionalDate": "1997-11-04T10:38:21Z"
+            }
+            """
+        let json = try XCTUnwrap(jsonStr.data(using: .utf8))
+        let model = try JSONDecoder().decode(Model.self, from: json)
+        let epoch: Double = 878639901
+        XCTAssertEqual(model.date.timeIntervalSince1970, epoch)
+        let encoded = try JSONEncoder().encode(model)
+        let customDecoder = JSONDecoder()
+        customDecoder.dateDecodingStrategy = .secondsSince1970
+        let newModel = try customDecoder.decode(MirrorModel.self, from: encoded)
+        XCTAssertEqual(newModel.date.timeIntervalSince1970, epoch)
+    }
+
+    func testPropertyWrapperCoding() throws {
+        let jsonStr = """
+            {
+                "int": 100
+            }
+            """
+        let json = try XCTUnwrap(jsonStr.data(using: .utf8))
+        let model = try JSONDecoder().decode(PropModel.self, from: json)
+        XCTAssertEqual(model.int, 5)
+        let encoded = try JSONEncoder().encode(model)
+        let obj = try JSONSerialization.jsonObject(with: encoded)
+        let dict = try XCTUnwrap(obj as? [String: Any])
+        XCTAssertEqual(dict["int"] as? Int, 5)
+    }
+}
+
+@Codable
+fileprivate struct Model {
+    @CodedBy(
+        ConditionalCoder(
+            decoder: ISO8601DateCoder(),
+            encoder: Since1970DateCoder()
+        )
+    )
+    let date: Date
+    @CodedBy(
+        ConditionalCoder(
+            decoder: ISO8601DateCoder(),
+            encoder: Since1970DateCoder()
+        )
+    )
+    let optionalDate: Date?
+}
+
+fileprivate struct MirrorModel: Codable {
+    let date: Date
+    let optionalDate: Date?
+}
+
+@Codable
+fileprivate struct PropModel {
+    @CodedBy(PropertyWrapperCoder<ConstIntCoder>())
+    let int: Int
+}
+
+@propertyWrapper
+struct ConstIntCoder: PropertyWrappable {
+    var wrappedValue: Int { 5 }
+
+    init(wrappedValue: Int) {}
+
+    func encode(to encoder: Encoder) throws {
+        try wrappedValue.encode(to: encoder)
+    }
+}