#9 Add Support for Custom Formatter

README.md

@@ -170,7 +170,7 @@ print(dates.rfc3339Date.description) // Prints "1996-12-20 00:39:57 +0000"
 print(dates.timestamp.description) // Prints "2001-01-01 00:00:00 +0000"
 ````
 
-Note that there's no built-in support for ISO8601 dates with precision greater than millisecond (e.g. microsecond or nanosecond), because Apple doesn't officially supports such precision natively, yet. Should you feel the necessity to have those, PRs are always welcome!
+Note that there's no built-in support for ISO8601 dates with precision greater than millisecond (e.g. microsecond or nanosecond), because Apple doesn't officially supports such precision natively, yet. Should you feel the necessity to have those, or any other custom date formatter, you can implement your own `DateConvertible` and use `.custom(dateConvertible)` DateCodingStrategy. If you think your use case should make its way into the official library, PRs are always welcome!
 
 ## Advanced Usage
 

Sources/Wrappers/CodableDate.swift

@@ -84,6 +84,9 @@ public enum DateCodingStrategy {
     case rfc3339
     /// Time interval since 1970.
     case timestamp
+    /// A custom date parser to be used, instead of a string formatter.
+    /// - Note: it's strongly advised that your implementation of DateConvertible converts to and from Date in a lossless manner, although not required.
+    case custom(DateConvertible)
 
     public func date(from value: String) -> Date? {
         switch self {
@@ -95,6 +98,7 @@ public enum DateCodingStrategy {
         case .timestamp:
             guard let timestamp = Double(value) else { return nil }
             return Date(timeIntervalSince1970: timestamp)
+        case let .custom(parser): return parser.date(from: value)
         }
     }
 
@@ -106,6 +110,7 @@ public enum DateCodingStrategy {
         case .rfc2822: return DateCodingStrategy.rfc2822Formatter.string(from: date)
         case .rfc3339: return DateCodingStrategy.rfc3339Formatter.string(from: date)
         case .timestamp: return "\(date.timeIntervalSince1970)"
+        case let .custom(parser): return parser.string(from: date)
         }
     }
 
@@ -134,6 +139,11 @@ public enum DateCodingStrategy {
     }
 }
 
+public protocol DateConvertible {
+    func date(from value: String) -> Date?
+    func string(from date: Date) -> String
+}
+
 // MARK: Equatable Conformance
 
 extension CodableDate: Equatable where T: Equatable {

Tests/KodableTests.swift

@@ -602,6 +602,16 @@ final class KodableTests: XCTestCase {
     }
 
     func testCodableDate() throws {
+        struct MyDateParser: DateConvertible {
+            func date(from _: String) -> Date? {
+                Date(timeIntervalSince1970: 123)
+            }
+
+            func string(from _: Date) -> String {
+                "Kodable"
+            }
+        }
+
         struct Dates: Kodable {
             @CodableDate(decoding: .enforceType) var iso8601: Date
             @CodableDate("iso8601") var isoDate: Date?
@@ -611,6 +621,7 @@ final class KodableTests: XCTestCase {
             @CodableDate(.rfc3339, "rfc3339") var rfc3339Date: Date
             @CodableDate(.timestamp, "timestamp", decoding: .lossless) var nonOptionalTimestamp: Date
             @CodableDate(.timestamp, "timestamp", decoding: .lossless) var timestamp: Date?
+            @CodableDate(.custom(MyDateParser()), "custom_date") var customDate: Date?
             @CodableDate var optionalDate: Date?
 
             @CodableDate(.timestamp, "timestamp_non_existent", default: KodableTests.testDate)
@@ -645,6 +656,7 @@ final class KodableTests: XCTestCase {
         XCTAssertEqual(decoded.rfc3339Date.description, "1996-12-20 00:39:57 +0000")
         XCTAssertEqual(decoded.nonOptionalTimestamp.description, "2001-01-01 00:00:00 +0000")
         XCTAssertEqual(decoded.timestamp?.description, "2001-01-01 00:00:00 +0000")
+        XCTAssertEqual(decoded.customDate?.description, "1970-01-01 00:02:03 +0000")
         XCTAssertEqual(decoded.defaultTimestamp.description, KodableTests.testDate.description)
         XCTAssertEqual(decoded.optionalDate, nil)
         XCTAssertEqual(decoded.ignoredDate, nil)
@@ -659,6 +671,7 @@ final class KodableTests: XCTestCase {
         XCTAssertEqual(newObject.rfc3339Date.description, "1996-12-20 00:39:57 +0000")
         XCTAssertEqual(newObject.nonOptionalTimestamp.description, "2001-01-01 00:00:00 +0000")
         XCTAssertEqual(newObject.timestamp?.description, "2001-01-01 00:00:00 +0000")
+        XCTAssertEqual(newObject.customDate?.description, "1970-01-01 00:02:03 +0000")
         XCTAssertEqual(newObject.defaultTimestamp.description, KodableTests.testDate.description)
         XCTAssertEqual(newObject.optionalDate, nil)
         XCTAssertEqual(newObject.ignoredDate, nil)
@@ -784,6 +797,7 @@ final class KodableTests: XCTestCase {
         "rfc2822": "Thu, 19 Dec 1996 16:39:57 GMT",
         "rfc3339": "1996-12-19T16:39:57-08:00",
         "timestamp": 978_307_200.0,
+        "custom_date": "lorem ipsum",
         "id": 2_623_488,
         "title": "     Create New Project       ",
         "empty": "       ",