Updated README

Sources/ObjectState.swift

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+//
+//  ObjectState.swift
+//  CoreStore
+//
+//  Copyright © 2021 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+#if canImport(Combine) && canImport(SwiftUI)
+
+import Combine
+import SwiftUI
+
+
+// MARK: - ObjectState
+
+/**
+ A property wrapper type that can read `ObjectPublisher` changes.
+ */
+@propertyWrapper
+@available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 10.15, *)
+public struct ObjectState<O: DynamicObject>: DynamicProperty {
+    
+    // MARK: Public
+    
+    /**
+     Creates an instance that observes `ObjectPublisher` changes and exposes an `Optional<ObjectSnapshot<O>>` value.
+     ```
+     @ObjectState
+     var person: ObjectSnapshot<Person>?
+     
+     init(objectPublisher: ObjectPublisher<Person>) {
+     
+        self._person = .init(objectPublisher)
+     }
+     
+     var body: some View {
+     
+        HStack {
+     
+            AsyncImage(self.person?.$avatarURL)
+            Text(self.person?.$fullName ?? "")
+        }
+     }
+     ```
+     
+     - parameter objectPublisher: The `ObjectPublisher` that the `ObjectState` will observe changes for
+     */
+    public init(_ objectPublisher: ObjectPublisher<O>?) {
+        
+        self.observer = .init(objectPublisher: objectPublisher)
+    }
+    
+    
+    // MARK: @propertyWrapper
+    
+    public var wrappedValue: ObjectSnapshot<O>? {
+        
+        return self.observer.item
+    }
+    
+    public var projectedValue: ObjectPublisher<O>? {
+        
+        return self.observer.objectPublisher
+    }
+    
+    
+    // MARK: DynamicProperty
+    
+    public mutating func update() {
+        
+        self._observer.update()
+    }
+    
+    
+    // MARK: Private
+    
+    @ObservedObject
+    private var observer: Observer
+    
+    
+    // MARK: - Observer
+    
+    private final class Observer: ObservableObject {
+        
+        @Published
+        var item: ObjectSnapshot<O>?
+        
+        let objectPublisher: ObjectPublisher<O>?
+        
+        init(objectPublisher: ObjectPublisher<O>?) {
+
+            guard
+                let dataStack = objectPublisher?.cs_dataStack(),
+                let objectPublisher = objectPublisher?.asPublisher(in: dataStack)
+            else {
+
+                self.objectPublisher = nil
+                self.item = nil
+                return
+            }
+            
+            self.objectPublisher = objectPublisher
+            self.item = objectPublisher.snapshot
+            
+            objectPublisher.addObserver(self) { [weak self] (objectPublisher) in
+                
+                guard let self = self else {
+                    
+                    return
+                }
+                self.item = objectPublisher.snapshot
+            }
+        }
+        
+        deinit {
+            
+            self.objectPublisher?.removeObserver(self)
+        }
+    }
+}
+
+#endif