Addressing State being consistent in value from the first check (#90)

* Update README.md

- change variable appState name to usernameState to reflect the value of the variable.

* Update README.md

- update appState variable name to usernameState for the whole read and write section

* Made changes to State to cache value when it is first retrieved.
Added a test to ensure that state value is consistent from when it is first checked

* Made additions to testStateClosureCachesValueOnGet to account for async

Sources/AppState/Application/Types/State/Application+State.swift

@@ -20,8 +20,36 @@ extension Application {
                         scope.key,
                         as: State<Value>.self
                     )
-                else { return _value }
+                else {
+                    defer {
+                        #if !os(Linux) && !os(Windows)
+                        Task {
+                            await MainActor.run {
+                                shared.cache.set(
+                                    value: Application.State(
+                                        type: .state,
+                                        initial: _value,
+                                        scope: scope
+                                    ),
+                                    forKey: scope.key
+                                )
+                            }
+                        }
+
+                        #else
+                        shared.cache.set(
+                            value: Application.State(
+                                type: .state,
+                                initial: _value,
+                                scope: scope
+                            ),
+                            forKey: scope.key
+                        )
 
+                        #endif
+                    }
+                    return _value
+                }
                 return state._value
             }
             set {

Tests/AppStateTests/AppStateTests.swift

@@ -13,7 +13,9 @@ fileprivate extension Application {
     var username: State<String> {
         state(initial: "Leif")
     }
-
+    var date: State<Date> {
+        state(initial: Date())
+    }
     var colors: State<[String: String]> {
         state(initial: ["primary": "#A020F0"])
     }
@@ -69,6 +71,23 @@ final class AppStateTests: XCTestCase {
         XCTAssertEqual(appState.value, "0xL")
         XCTAssertEqual(Application.state(\.username).value, "0xL")
     }
+
+    func testStateClosureCachesValueOnGet() async {
+        let dateState: Application.State = Application.state(\.date)
+        #if !os(Linux) && !os(Windows)
+        await MainActor.run {
+            let copyOfDateState: Application.State =
+            Application.state(\.date)
+
+            XCTAssertEqual(copyOfDateState.value, dateState.value)
+        }
+        #else
+        let copyOfDateState: Application.State =
+        Application.state(\.date)
+
+        XCTAssertEqual(copyOfDateState.value, dateState.value)
+        #endif
+    }
 
     func testPropertyWrappers() {
         let exampleView = ExampleView()