Update StoredLocationBase implementation

Author: Kyle-Ye

Package.resolved

@@ -16,7 +16,7 @@ class AnyLocation<Value>: AnyLocationBase {
     }
     func get() -> Value { fatalError() }
     func set(_ value: Value, transaction: Transaction) { fatalError() }
-    func projecting<P>(_ p: P) -> AnyLocation<P.Projected> where P: Projection, P.Base == Value {
+    func projecting<P: Projection>(_ p: P) -> AnyLocation<P.Projected> where Value == P.Base {
         fatalError()
     }
     func update() -> (Value, Bool) { fatalError() }

Sources/OpenSwiftUI/Core/Data/Location/AnyLocation.swift

@@ -27,8 +27,8 @@ class LocationBox<L: Location>: AnyLocation<L.Value> {
         location.set(value, transaction: transaction)
     }
 
-    override func projecting<P>(_ p: P) -> AnyLocation<P.Projected> where L.Value == P.Base, P : Projection {
-        cache.reference(for: p, on: location)
+    override func projecting<P: Projection>(_ projection: P) -> AnyLocation<P.Projected> where L.Value == P.Base {
+        cache.reference(for: projection, on: location)
     }
 
     override func update() -> (L.Value, Bool) {

Sources/OpenSwiftUI/Core/Data/Location/LocationBox.swift

@@ -6,7 +6,10 @@
 //  Status: WIP
 //  ID: EBDC911C9EE054BAE3D86F947C24B7C3
 
-class StoredLocationBase<Value>: AnyLocation<Value> {
+internal import OpenGraphShims
+internal import COpenSwiftUI
+
+class StoredLocationBase<Value>: AnyLocation<Value>, Location {
     private struct LockedData {
         var currentValue: Value
         var savedValue: [Value]
@@ -53,12 +56,80 @@ class StoredLocationBase<Value>: AnyLocation<Value> {
         super.init()
     }
 
+    private var isValid: Bool {
+        true
+    }
+    
+    // MARK: - abstract method
+    
+    private var isUpdating: Bool {
+        fatalError("abstract")
+    }
+    
+    private func commit(transaction: Transaction, mutation: BeginUpdate) {
+        fatalError("abstract")
+    }
+    
+    private func notifyObservers() {
+        fatalError("abstract")
+    }
+    
+    // MARK: - AnyLocation
+    
+    override var wasRead: Bool {
+        get { _wasRead }
+        set { _wasRead = newValue }
+    }
+    
+    override func get() -> Value {
+        data.currentValue
+    }
+    
+    override func set(_ value: Value, transaction: Transaction) {
+        guard !isUpdating else {
+            Log.runtimeIssues("Modifying state during view update, this will cause undefined behavior.")
+            return
+        }
+        guard isValid else {
+            $data.withMutableData { data in
+                data.savedValue.removeAll()
+            }
+            return
+        }
+        let _ = $data.withMutableData { data in
+            guard !compareValues(data.currentValue, value) else {
+                return false
+            }
+            data.savedValue.append(data.currentValue)
+            data.currentValue = value
+            return true
+        }
+        // TODO
+    }
+    
+    override func projecting<P: Projection>(_ projection: P) -> AnyLocation<P.Projected> where Value == P.Base {
+        data.cache.reference(for: projection, on: self)
+    }
+    
+    override func update() -> (Value, Bool) {
+        _wasRead = true
+        return (updateValue, true)
+    }
+    
+    // MARK: - final properties and methods
+    
     deinit {
         $data.destroy()
     }
 
-    private func beginUpdate() {
-        // TODO
+    final var updateValue: Value {
+        $data.withMutableData { data in
+            data.savedValue.first ?? data.currentValue
+        }
+    }
+    
+    private final func beginUpdate() {
+        data.savedValue.removeFirst()
     }
 }