feat(*): Add default argument to Map's value(_)

Author: emrcftci

README.md

@@ -248,6 +248,7 @@ init(map: Map) throws {
     createdAt = try map.value("createdAt", using: DateTransform()) // throws an error when it fails
     updatedAt = try? map.value("updatedAt", using: DateTransform()) // optional
     posts     = (try? map.value("posts")) ?? [] // optional + default value
+    surname    = try? map.value("surname", default: "DefaultSurname") // optional + default value as an argument
 }
 ```
 

Sources/Map.swift

@@ -202,3 +202,45 @@ private func valueFor(_ keyPathComponents: ArraySlice<String>, array: [Any]) ->
 
 	return (false, nil)
 }
+
+// MARK: - Default Value
+
+public extension Map {
+
+	/// Returns `default` value if there is nothing to parse.
+  func value<T>(_ key: String, default: T.Object, using transform: T) throws -> T.Object where T: TransformType {
+    if let value: T.Object = try? self.value(key, using: transform) {
+      return value
+    } else {
+      return `default`
+    }
+  }
+
+	/// Returns `default` value if there is nothing to parse.
+  func value<T>(_ key: String, default: T) throws -> T {
+    if let value: T = try? self.value(key) {
+      return value
+    } else {
+      return `default`
+    }
+  }
+
+	/// Returns `default` value if there is nothing to parse.
+  func value<T: BaseMappable>(_ key: String, default: [T]) -> [T] {
+    do {
+      let value: [T] = try self.value(key)
+      return value
+    } catch {
+      return `default`
+    }
+  }
+
+	/// Returns `default` value if there is nothing to parse.
+  func value<T>(_ key: String, default: T) throws -> T where T: BaseMappable {
+    if let value: T = try? self.value(key) as T {
+      return value
+    } else {
+      return `default`
+    }
+  }
+}

Tests/ObjectMapperTests/MapContextTests.swift

@@ -242,6 +242,32 @@ class MapContextTests: XCTestCase {
 
 		XCTFail()
 	}
+
+	func testDefaultArgumentWithoutValue() {
+		let JSON: [String: Any] = [:]
+		let dog = try? Mapper<ImmutableDog>().map(JSON: JSON) as ImmutableDog
+
+		XCTAssertNotNil(dog)
+		XCTAssertTrue(dog!.name == "Sasha")
+	}
+
+	func testDefaultArgumentWithValue() {
+		let JSON = ["name": "Sofie"]
+		let dog = try? Mapper<ImmutableDog>().map(JSON: JSON) as ImmutableDog
+
+		XCTAssertNotNil(dog)
+		XCTAssertTrue(dog!.name == "Sofie")
+	}
+
+	// MARK: - Default Argument
+	public struct ImmutableDog: ImmutableMappable {
+		public let name: String
+
+		/// Define `default` value to use if it is nothing to parse in `name`
+		public init(map: Map) throws {
+			name = try map.value("name", default: "Sasha")
+		}
+	}
 
 	// MARK: - Nested Types
 	// MARK: BaseMappable