added type-erasers for CoreStoreObject property containers

Sources/AnyCoreStoreKeyPath.swift

@@ -0,0 +1,83 @@
+//
+//  AnyCoreStoreKeyPath.swift
+//  CoreStore
+//
+//  Created by John Estropia on 2017/10/02.
+//  Copyright © 2017 John Rommel Estropia. All rights reserved.
+//
+
+import Foundation
+
+
+// MARK: - AnyCoreStoreKeyPath
+
+public protocol AnyCoreStoreKeyPath {
+    
+    var cs_keyPathString: String { get }
+}
+
+// SE-0143 is not implemented: https://github.com/apple/swift-evolution/blob/master/proposals/0143-conditional-conformances.md
+//extension KeyPath: AnyCoreStoreKeyPath where Root: NSManagedObject, Value: ImportableAttributeType {
+//
+//    public var cs_keyPathString: String {
+//
+//        return self._kvcKeyPathString!
+//    }
+//}
+
+extension ValueContainer.Required: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+    
+        return self.keyPath
+    }
+}
+
+extension ValueContainer.Optional: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+
+extension TransformableContainer.Required: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+
+extension TransformableContainer.Optional: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+
+extension RelationshipContainer.ToOne: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+
+extension RelationshipContainer.ToManyOrdered: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+
+extension RelationshipContainer.ToManyUnordered: AnyCoreStoreKeyPath {
+    
+    public var cs_keyPathString: String {
+        
+        return self.keyPath
+    }
+}
+