WIP: reorganization of keypath utilities (in prep for @propertyWrappers)

Sources/String+KeyPaths.swift

@@ -0,0 +1,66 @@
+//
+//  String+KeyPaths.swift
+//  CoreStore
+//
+//  Copyright © 2019 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.
+//
+
+import CoreData
+import Foundation
+
+
+// MARK: - KeyPathString
+
+extension KeyPathString {
+
+    /**
+     Extracts the keyPath string from the property.
+     ```
+     let keyPath = String(keyPath: \Person.nickname)
+     ```
+     */
+    public init<O: NSManagedObject, V: AllowedObjectiveCKeyPathValue>(keyPath: KeyPath<O, V>) {
+
+        self = keyPath.cs_keyPathString
+    }
+
+    /**
+     Extracts the keyPath string from the property.
+     ```
+     let keyPath = String(keyPath: \Person.nickname)
+     ```
+     */
+    public init<O: CoreStoreObject, K: KeyPathStringConvertible>(keyPath: KeyPath<O, K>) {
+
+        self = O.meta[keyPath: keyPath].cs_keyPathString
+    }
+
+    /**
+     Extracts the keyPath string from the property.
+     ```
+     let keyPath = String(keyPath: \Person.nickname)
+     ```
+     */
+    public init<O: DynamicObject, T, V>(keyPath: Where<O>.Expression<T, V>) {
+
+        self = keyPath.cs_keyPathString
+    }
+}