Added KVO support via NSObject.currentValuePublisher(for:)

Sources/CombineExtensions/CurrentValuePublisher/CurrentValuePublisher+KVO.swift

@@ -0,0 +1,26 @@
+import Foundation
+
+public protocol KVOCurrentValuePublishing {}
+
+extension NSObject: KVOCurrentValuePublishing {}
+
+extension KVOCurrentValuePublishing where Self: NSObject {
+
+    /// Returns a `CurrentValuePublisher` that tracks the current value of a KVO-compliant property.
+    ///
+    /// - Parameter keyPath: The key path of the property to observe.
+    /// - Returns: A `CurrentValuePublisher` that tracks the property's value.
+    ///
+    /// This implementation follows the approach of `NSObject.publisher(for:options:)` from Foundation,
+    /// previously available in the [swift-corelibs-foundation](https://bit.ly/nsobject-keyvalueobserving)
+    /// open source repository.
+    public func currentValuePublisher<Value>(
+        for keyPath: KeyPath<Self, Value>
+    ) -> CurrentValuePublisher<Value, Never> {
+        return CurrentValuePublisher(
+            initial: self[keyPath: keyPath],
+            upstream: self.publisher(for: keyPath, options: .new)
+        )
+    }
+
+}