Add support for ISO-8601-formatted dates (#8)

Add support for ISO-8601-formatted dates

This change adds support for the common `ISO-8601` date format, by making
it possible to pass a `ISO8601DateFormatter` when encoding or decoding a
date (on supported platforms).

Sources/Codextended/Codextended.swift

@@ -49,13 +49,13 @@ public extension Encoder {
 
     /// Encode a date for a given key (specified as a string), using a specific formatter.
     /// To encode a date without using a specific formatter, simply encode it like any other value.
-    func encode(_ date: Date, for key: String, using formatter: DateFormatter) throws {
+    func encode<F: AnyDateFormatter>(_ date: Date, for key: String, using formatter: F) throws {
         try encode(date, for: AnyCodingKey(key), using: formatter)
     }
 
     /// Encode a date for a given key (specified using a `CodingKey`), using a specific formatter.
     /// To encode a date without using a specific formatter, simply encode it like any other value.
-    func encode<K: CodingKey>(_ date: Date, for key: K, using formatter: DateFormatter) throws {
+    func encode<K: CodingKey, F: AnyDateFormatter>(_ date: Date, for key: K, using formatter: F) throws {
         let string = formatter.string(from: date)
         try encode(string, for: key)
     }
@@ -106,14 +106,14 @@ public extension Decoder {
     /// Decode a date from a string for a given key (specified as a string), using a
     /// specific formatter. To decode a date using the decoder's default settings,
     /// simply decode it like any other value instead of using this method.
-    func decode(_ key: String, using formatter: DateFormatter) throws -> Date {
+    func decode<F: AnyDateFormatter>(_ key: String, using formatter: F) throws -> Date {
         return try decode(AnyCodingKey(key), using: formatter)
     }
 
     /// Decode a date from a string for a given key (specified as a `CodingKey`), using
     /// a specific formatter. To decode a date using the decoder's default settings,
     /// simply decode it like any other value instead of using this method.
-    func decode<K: CodingKey>(_ key: K, using formatter: DateFormatter) throws -> Date {
+    func decode<K: CodingKey, F: AnyDateFormatter>(_ key: K, using formatter: F) throws -> Date {
         let container = try self.container(keyedBy: K.self)
         let rawString = try container.decode(String.self, forKey: key)
 
@@ -129,6 +129,24 @@ public extension Decoder {
     }
 }
 
+// MARK: - Date formatters
+
+/// Protocol acting as a common API for all types of date formatters,
+/// such as `DateFormatter` and `ISO8601DateFormatter`.
+public protocol AnyDateFormatter {
+    /// Format a string into a date
+    func date(from string: String) -> Date?
+    /// Format a date into a string
+    func string(from date: Date) -> String
+}
+
+extension DateFormatter: AnyDateFormatter {}
+
+@available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
+extension ISO8601DateFormatter: AnyDateFormatter {}
+
+// MARK: - Private supporting types
+
 private struct AnyCodingKey: CodingKey {
     var stringValue: String
     var intValue: Int?

Tests/CodextendedTests/CodextendedTests.swift

@@ -127,6 +127,35 @@ final class CodextendedTests: XCTestCase {
                        formatter.string(from: valueB.date))
     }
 
+    @available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
+    func testDateWithISO8601Formatter() throws {
+        struct Value: Codable, Equatable {
+            let date: Date
+
+            init(date: Date) {
+                self.date = date
+            }
+
+            init(from decoder: Decoder) throws {
+                let formatter = ISO8601DateFormatter()
+                date = try decoder.decode("key", using: formatter)
+            }
+
+            func encode(to encoder: Encoder) throws {
+                let formatter = ISO8601DateFormatter()
+                try encoder.encode(date, for: "key", using: formatter)
+            }
+        }
+
+        let valueA = Value(date: Date())
+        let data = try valueA.encoded()
+        let valueB = try data.decoded() as Value
+        let formatter = ISO8601DateFormatter()
+
+        XCTAssertEqual(formatter.string(from: valueA.date),
+                       formatter.string(from: valueB.date))
+    }
+
     func testDecodingErrorThrownForInvalidDateString() {
         struct Value: Decodable {
             let date: Date
@@ -149,7 +178,7 @@ final class CodextendedTests: XCTestCase {
     }
 
     func testAllTestsRunOnLinux() {
-        verifyAllTestsRunOnLinux()
+        verifyAllTestsRunOnLinux(excluding: ["testDateWithISO8601Formatter"])
     }
 }
 

Tests/CodextendedTests/LinuxTestable.swift

@@ -11,7 +11,7 @@ protocol LinuxTestable: XCTestCase {
 }
 
 extension LinuxTestable {
-    func verifyAllTestsRunOnLinux() {
+    func verifyAllTestsRunOnLinux(excluding excludedTestNames: Set<String>) {
         #if os(macOS)
         let testNames = Set(Self.allTests.map { $0.0 })
 
@@ -20,6 +20,10 @@ extension LinuxTestable {
                 continue
             }
 
+            guard !excludedTestNames.contains(name) else {
+                continue
+            }
+
             if !testNames.contains(name) {
                 XCTFail("""
                 Test case \(Self.self) does not include test \(name) on Linux.