Experimental property wrapper

Author: lukeredpath

.swiftpm/xcode/xcshareddata/xcschemes/swift-coding.xcscheme

@@ -0,0 +1,91 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1250"
+   version = "1.3">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "Coding"
+               BuildableName = "Coding"
+               BlueprintName = "Coding"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </BuildActionEntry>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "NO"
+            buildForArchiving = "NO"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "CodingTests"
+               BuildableName = "CodingTests"
+               BlueprintName = "CodingTests"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES">
+      <Testables>
+         <TestableReference
+            skipped = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "CodingTests"
+               BuildableName = "CodingTests"
+               BlueprintName = "CodingTests"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "Coding"
+            BuildableName = "Coding"
+            BlueprintName = "Coding"
+            ReferencedContainer = "container:">
+         </BuildableReference>
+      </MacroExpansion>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

Sources/Coding/Encoding.swift

@@ -159,3 +159,20 @@ public extension Encoding {
         }
     }
 }
+
+// MARK: - Property Wrapper
+
+@propertyWrapper
+public struct UsesEncoding<Value>: Encodable {
+    public let wrappedValue: Value
+    public let encoding: Encoding<Value>
+
+    public init(wrappedValue: Value, _ encoding: Encoding<Value>) {
+        self.wrappedValue = wrappedValue
+        self.encoding = encoding
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        try encoding.encode(wrappedValue, encoder)
+    }
+}

Tests/CodingTests/EncodingTests.swift

@@ -534,6 +534,35 @@ final class EncodingTests: XCTestCase {
         )
     }
 
+    // MARK: - Encoding Property Wrapper
+
+    func testEncodingPropertyWrapper() {
+        struct User: Encodable {
+            @UsesEncoding(.lowercased)
+            var id: UUID = UUID()
+
+            @UsesEncoding(.lowercased)
+            var name: String = ""
+        }
+
+        encoder.outputFormatting = .prettyPrinted
+
+        let user = User(
+            id: UUID(uuidString: "3B0B3AFC-4C61-4251-8FC5-F046D06DC3EC")!,
+            name: "Joe Bloggs"
+        )
+
+        XCTAssertEqual(
+            """
+            {
+              "id" : "3b0b3afc-4c61-4251-8fc5-f046d06dc3ec",
+              "name" : "joe bloggs"
+            }
+            """,
+            stringValue(try encoder.encode(user))
+        )
+    }
+
     private func stringValue(_ data: Data) -> String {
         String(data: data, encoding: .utf8)!
     }
@@ -573,6 +602,18 @@ struct Manufacturer {
     }
 }
 
+extension Encoding where Value == String {
+    static let lowercased: Self = Encoding<String>
+        .singleValue
+        .pullback { $0.lowercased() }
+}
+
+extension Encoding where Value == UUID {
+    static let lowercased: Self = Encoding<String>
+        .lowercased
+        .pullback { $0.uuidString }
+}
+
 extension Encoding where Value == Manufacturer {
     static let name: Self = Encoding<String>
         .withKey(Model.CodingKeys.name)