Added read-only dynamic member lookup support to ListProperties

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Fixed
 
+- Fixed a confusing compilation error when omitting the `.content` property on read-only `KeyPath` lookups on `ListProperties`. 
+
 ### Added
 
 ### Removed

ListableUI/Sources/ListProperties.swift

@@ -196,6 +196,31 @@ import UIKit
         configure(&self)
     }
 
+    //
+    // MARK: Reading Content
+    //
+
+    /// Allows directly reading properties on the list's `Content`, without having to explicitly specify
+    /// the `.content` component.
+    ///
+    /// Eg, you can now replace:
+    /// ```
+    /// ListProperties { list in
+    ///     ... = list.content.firstItem
+    ///     ... = list.content.lastItem
+    /// }
+    /// ```
+    /// With:
+    /// ```
+    /// ListProperties { list in
+    ///     ... = list.firstItem
+    ///     ... = list.lastItem
+    /// }
+    /// ```
+    public subscript<Value>(dynamicMember keyPath: KeyPath<Content, Value>) -> Value {
+        get { self.content[keyPath: keyPath] }
+    }
+
     //
     // MARK: Adding Content
     //
@@ -208,15 +233,13 @@ import UIKit
     /// ListProperties { list in
     ///     list.content.header = ...
     ///     list.content.footer = ...
-    ///     ...
     /// }
     /// ```
     /// With:
     /// ```
     /// ListProperties { list in
     ///     list.header = ...
     ///     list.footer = ...
-    ///     ...
     /// }
     /// ```
     public subscript<Value>(dynamicMember keyPath: WritableKeyPath<Content, Value>) -> Value {

ListableUI/Tests/ListPropertiesTests.swift

@@ -5,9 +5,37 @@
 //  Created by Kyle Van Essen on 11/27/19.
 //
 
+import ListableUI
 import XCTest
 
 class ListPropertiesTests : XCTestCase
 {
-
+    private func properties() -> ListProperties {
+        ListProperties(
+            animatesChanges: true,
+            layout: .flow(),
+            appearance: .init(),
+            scrollIndicatorInsets: .zero,
+            behavior: .init(),
+            autoScrollAction: .none,
+            accessibilityIdentifier: "",
+            debuggingIdentifier: "") { _ in }
+    }
+
+    func test_read_only_dynamic_member_lookup() {
+        let properties = properties()
+        // Ensure that this compiles. Previously we were missing the read-only KeyPath
+        // dynamicMember subscript implementation which would lead to this error:
+        // Cannot assign to property: 'lastItem' is a get-only property
+        let item = properties.lastItem
+        XCTAssertNil(item)
+    }
+
+    func test_writeable_dynamic_member_lookup() {
+        var properties = properties()
+        // Ensure that this compiles and writes through to the underlying content.
+        properties.identifier = "Hello"
+        XCTAssertEqual(properties.identifier, "Hello")
+        XCTAssertEqual(properties.identifier, properties.content.identifier)
+    }
 }