Add lazy sequence decoder

Author: josh

sources/declarative/decodable/Decoder.swift

@@ -60,4 +60,22 @@ extension CSVDecoder {
         let source = ShadowDecoder.Source(reader: reader, configuration: self.configuration, userInfo: self.userInfo)
         return try T(from: ShadowDecoder(source: source, codingPath: []))
     }
+
+    /// Returns a sequence for decoding each row from a CSV file (given as a `Data` blob).
+    /// - parameter data: The data blob representing a CSV file.
+    /// - throws: `CSVError<CSVReader>` exclusively.
+    open func lazy(from data: Data) throws -> CSVDecoderSequence {
+        let reader = try CSVReader(input: data, configuration: self.configuration.readerConfiguration)
+        let source = ShadowDecoder.Source(reader: reader, configuration: self.configuration, userInfo: self.userInfo)
+        return CSVDecoderSequence(source: source)
+    }
+
+    /// Returns a sequence for decoding each row from a CSV file (being pointed by `url`).
+    /// - parameter url: The URL pointing to the file to decode.
+    /// - throws: `CSVError<CSVReader>` exclusively.
+    open func lazy(from url: URL) throws -> CSVDecoderSequence {
+        let reader = try CSVReader(input: url, configuration: self.configuration.readerConfiguration)
+        let source = ShadowDecoder.Source(reader: reader, configuration: self.configuration, userInfo: self.userInfo)
+        return CSVDecoderSequence(source: source)
+    }
 }

sources/declarative/decodable/DecoderSequence.swift

@@ -0,0 +1,31 @@
+open class CSVDecoderSequence: IteratorProtocol, Sequence {
+    private let source: ShadowDecoder.Source
+    private var currentIndex: Int = 0
+
+    init(source: ShadowDecoder.Source) {
+        self.source = source
+    }
+
+    /// Advances to the next row and returns a `CSVRowDecoder`, or `nil` if no next row exists.
+    public func next() -> CSVRowDecoder? {
+        guard !self.source.isRowAtEnd(index: self.currentIndex) else {
+            return nil
+        }
+
+        defer { self.currentIndex += 1 }
+        let decoder = ShadowDecoder(source: source, codingPath: [IndexKey(self.currentIndex)])
+        return CSVRowDecoder(decoder: decoder)
+    }
+}
+
+public struct CSVRowDecoder {
+    /// The representation of the decoding process point-in-time.
+    let decoder: ShadowDecoder
+
+    /// Returns a value of the type you specify, decoded from CSV row.
+    /// - parameter type: The type of the value to decode from the supplied file.
+    /// - throws: `DecodingError`, or `CSVError<CSVReader>`, or the error raised by your custom types.
+    public func decode<T:Decodable>(_ type: T.Type) throws -> T {
+        return try T(from: decoder)
+    }
+}

tests/CodableTests/DecodingRegularUsageTests.swift

@@ -91,6 +91,16 @@ extension DecodingRegularUsageTests {
                 XCTAssertEqual(pet.gender?.rawValue ?? "", testPet[3])
                 XCTAssertEqual(pet.animal, testPet[4])
             }
+
+            for (index, row) in try decoder.lazy(from: input).enumerated() {
+                let pet = try row.decode(Pet.self)
+                let testPet = TestData.content[index]
+                XCTAssertEqual(pet.sequence, Int(testPet[0])!)
+                XCTAssertEqual(pet.name, testPet[1])
+                XCTAssertEqual(pet.age, Double(testPet[2])!)
+                XCTAssertEqual(pet.gender?.rawValue ?? "", testPet[3])
+                XCTAssertEqual(pet.animal, testPet[4])
+            }
         }
     }