Add optionalFrom for array of RawRepresentables (#125)

CHANGELOG.md

@@ -6,7 +6,9 @@
 
 ## Enhancements
 
-- None
+- Add `optionalFrom` for arrays of `RawRepresentable`s
+  [Keith Smiley](https://github.com/keith)
+  [#125](https://github.com/lyft/mapper/pull/125)
 
 # 7.2.0
 

Sources/Mapper.swift

@@ -95,6 +95,24 @@ public struct Mapper {
         return rawValues.flatMap { T(rawValue: $0) ?? defaultValue }
     }
 
+    /// Get an optional array of RawRepresentable values from a field in the the source data.
+    ///
+    /// - note: If T.init(rawValue:) fails given the T.RawValue from the array of source data, that value will
+    ///         be replaced by the passed defaultValue, which defaults to nil. The resulting array is
+    ///         flatMapped and all nils are removed. This means that any unrecognized values will be removed
+    ///         or replaced with the default. This ensures backwards compatibility if your source data has
+    ///         keys that your mapping layer doesn't know about yet.
+    ///
+    /// - parameter field:        The field to use from the source data
+    /// - parameter defaultValue: The value to use if the rawValue initializer fails
+    ///
+    /// - returns: An array of the RawRepresentable value, with all nils removed or nil if anything throws
+    public func optionalFrom<T: RawRepresentable>(_ field: String, defaultValue: T? = nil) ->
+        [T]? where T.RawValue: Convertible, T.RawValue == T.RawValue.ConvertedType
+    {
+        return try? self.from(field, defaultValue: defaultValue)
+    }
+
     // MARK: - T: Mappable
 
     /// Get a Mappable value from the given field in the source data

Tests/MapperTests/RawRepresentibleValueTests.swift

@@ -240,4 +240,34 @@ final class RawRepresentibleValueTests: XCTestCase {
             XCTFail("Expected no errors, got \(error)")
         }
     }
+
+    func testOptionalArrayRawValues() {
+        enum Value: String {
+            case first
+        }
+
+        let map = Mapper(JSON: ["values": ["first", "there"]])
+        let values: [Value]? = map.optionalFrom("values")
+        XCTAssertEqual(values ?? [], [.first])
+    }
+
+    func testOptionalArrayRawValuesMissingKey() {
+        enum Value: String {
+            case first
+        }
+
+        let map = Mapper(JSON: [:])
+        let values: [Value]? = map.optionalFrom("values")
+        XCTAssertNil(values)
+    }
+
+    func testOptionalArrayDefaultValues() {
+        enum Value: String {
+            case first
+        }
+
+        let map = Mapper(JSON: ["values": ["invalid"]])
+        let values: [Value]? = map.optionalFrom("values", defaultValue: .first)
+        XCTAssertEqual(values ?? [], [.first])
+    }
 }