Improve nesting

Sources/CodableCSV/Containers/DecodingStorage.swift

@@ -46,6 +46,9 @@ final class DecodingStorage {
         guard let value = dictionary[nesting.nest(codingPath: codingPath)] else {
             throw CSVCodingError.pathNotFound(codingPath)
         }
+        if none.decodeNil(value, codingPath: codingPath) {
+            throw CSVCodingError.couldNotDecode(value, as: String.self)
+        }
         return value
     }
 
@@ -56,7 +59,7 @@ final class DecodingStorage {
     func isAtEnd(codingPath: [CodingKey]) -> Bool {
         let key = nesting.nest(codingPath: codingPath)
         if let value = dictionary[key] {
-            return (try? none.decodeNil(value, codingPath: codingPath)) ?? true
+            return none.decodeNil(value, codingPath: codingPath)
         }
         return !dictionary.keys.contains(where: { $0.hasPrefix(key) })
     }

Sources/CodableCSV/Containers/KeyedDecoder.swift

@@ -41,6 +41,18 @@ extension KeyedDecoder: KeyedDecodingContainerProtocol {
         return try decoder.decode(T.self)
     }
 
+    func decodeIfPresent<T: Decodable>(_ type: T.Type, forKey key: Key) throws -> T? {
+        do {
+            return try decode(T.self, forKey: key)
+        } catch {
+            if try decodeNil(forKey: key) {
+                return nil
+            } else {
+                throw error
+            }
+        }
+    }
+
     // MARK: Methods - Containers
 
     func nestedContainer<NestedKey: CodingKey>(keyedBy type: NestedKey.Type,

Sources/CodableCSV/Options/None+Empty.swift

@@ -11,7 +11,7 @@ private struct EmptyStrategy: NoneStrategy {
         .init()
     }
 
-    func decodeNil(_ string: String, codingPath: [CodingKey]) throws -> Bool {
+    func decodeNil(_ string: String, codingPath: [CodingKey]) -> Bool {
         string.isEmpty
     }
 

Sources/CodableCSV/Options/None+Null.swift

@@ -13,7 +13,7 @@ private struct WordStrategy: NoneStrategy {
         word
     }
 
-    func decodeNil(_ string: String, codingPath: [CodingKey]) throws -> Bool {
+    func decodeNil(_ string: String, codingPath: [CodingKey]) -> Bool {
         string == word
     }
 

Sources/CodableCSV/Options/None.swift

@@ -7,7 +7,7 @@
 
 public protocol NoneStrategy {
     func encodeNil(codingPath: [CodingKey]) throws -> String
-    func decodeNil(_ string: String, codingPath: [CodingKey]) throws -> Bool
+    func decodeNil(_ string: String, codingPath: [CodingKey]) -> Bool
 }
 
 public struct CSVNone {

Tests/CodableCSVTests/CodableCSVTests.swift

@@ -102,6 +102,38 @@ final class CodableCSVTests: XCTestCase {
         }
     }
 
+    func testNesting3() {
+        struct InnerType: Codable, Equatable {
+            var name: String
+        }
+        struct OuterType: Codable, Equatable {
+            var age: Int
+            var inner: InnerType?
+        }
+        let objects = [OuterType(age: 10, inner: InnerType(name: "Paul")), OuterType(age: 12, inner: InnerType(name: "Peter")), OuterType(age: 15, inner: nil)]
+
+        let encodingExpectation = self.expectation(description: "encoder")
+        encodingExpectation.expectedFulfillmentCount = 2
+        var encoder = CSVEncoder()
+        encoder.register(for: InnerType.self) { inner in
+            encodingExpectation.fulfill()
+            return inner.name
+        }
+        var decoder = CSVDecoder()
+        decoder.register(InnerType.init)
+
+        let encoded = try! encoder.encode(objects)
+        wait(for: [encodingExpectation], timeout: 2)
+        print(String(data: encoded, encoding: .utf8) ?? "nil")
+        let decoded = try! decoder.decode(OuterType.self, from: encoded)
+        XCTAssertEqual(objects, decoded)
+
+        let o = (0..<100).flatMap { _ in objects }
+        measure {
+            measurableTest(objects: o)
+        }
+    }
+
     func testAllPrimitives() {
         struct TestType: Codable, Equatable {
             var bool: Bool?