improved API for custom getters and setters in Field properties

Sources/ObjectProxy.swift

@@ -0,0 +1,235 @@
+//
+//  ObjectProxy.swift
+//  CoreStore
+//
+//  Copyright © 2020 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: - ObjectProxy
+
+/**
+ An `ObjectProxy` is only used when overriding getters and setters for `CoreStoreObject` properties. Custom getters and setters are implemented as a closure that "overrides" the default property getter/setter. The closure receives an `ObjectProxy<O>`, which acts as a fast, type-safe KVC interface for `CoreStoreObject`. The reason a `CoreStoreObject` instance is not passed directly is because the Core Data runtime is not aware of `CoreStoreObject` properties' static typing, and so loading those info every time KVO invokes this accessor method incurs a heavy performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `ObjectProxy<O>.$property.primitiveValue` instead of `ObjectProxy<O>.$property.value`, which would execute the same accessor again recursively.
+ */
+@dynamicMemberLookup
+public struct ObjectProxy<O: CoreStoreObject> {
+
+    /**
+     Returns the value for the property identified by a given key.
+     */
+    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Stored<V>>) -> FieldProxy<V> {
+
+        return .init(rawObject: self.rawObject, keyPath: member)
+    }
+
+    /**
+     Returns the value for the property identified by a given key.
+     */
+    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Virtual<V>>) -> FieldProxy<V> {
+
+        return .init(rawObject: self.rawObject, keyPath: member)
+    }
+
+    /**
+     Returns the value for the property identified by a given key.
+     */
+    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Coded<V>>) -> FieldProxy<V> {
+
+        return .init(rawObject: self.rawObject, keyPath: member)
+    }
+
+
+    // MARK: Internal
+
+    internal let rawObject: CoreStoreManagedObject
+
+    internal init(_ rawObject: CoreStoreManagedObject) {
+
+        self.rawObject = rawObject
+    }
+
+
+    // MARK: - FieldProxy
+
+    public struct FieldProxy<V> {
+
+        // MARK: Public
+
+        /**
+         Returns the value for the specified property from the object’s private internal storage.
+
+         Accessing this property does not invoke the access notification methods (`willAccessValue(forKey:)` and `didAccessValue(forKey:)`). This method is used primarily to implement custom accessor methods that need direct access to the object's private storage.
+         */
+        public var primitiveValue: V? {
+
+            get {
+
+                return self.getPrimitiveValue()
+            }
+            nonmutating set {
+
+                self.setPrimitiveValue(newValue)
+            }
+        }
+
+        /**
+         Returns the value for the property identified by a given key.
+
+         Accessing this property triggers the access notification methods (`willAccessValue(forKey:)` and `didAccessValue(forKey:)`).
+         */
+        public var value: V {
+
+            get {
+
+                return self.getValue()
+            }
+            nonmutating set {
+
+                self.setValue(newValue)
+            }
+        }
+
+
+        // MARK: Internal
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Stored<V>>) {
+
+            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
+        }
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Virtual<V>>) {
+
+            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
+        }
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Coded<V>>) {
+
+            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
+        }
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Stored<V>) {
+
+            let keyPathString = field.keyPath
+            self.getValue = {
+
+                return FieldContainer<O>.Stored<V>.read(field: field, for: rawObject) as! V
+            }
+            self.setValue = {
+
+                FieldContainer<O>.Stored<V>.modify(field: field, for: rawObject, newValue: $0)
+            }
+            self.getPrimitiveValue = {
+
+                return V.cs_fromFieldStoredNativeType(
+                    rawObject.primitiveValue(forKey: keyPathString) as! V.FieldStoredNativeType
+                )
+            }
+            self.setPrimitiveValue = {
+
+                rawObject.setPrimitiveValue(
+                    $0.cs_toFieldStoredNativeType(),
+                    forKey: keyPathString
+                )
+            }
+        }
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Virtual<V>) {
+
+            let keyPathString = field.keyPath
+            self.getValue = {
+
+                return FieldContainer<O>.Virtual<V>.read(field: field, for: rawObject) as! V
+            }
+            self.setValue = {
+
+                FieldContainer<O>.Virtual<V>.modify(field: field, for: rawObject, newValue: $0)
+            }
+            self.getPrimitiveValue = {
+
+                switch rawObject.primitiveValue(forKey: keyPathString) {
+
+                case let value as V:
+                    return value
+
+                case nil,
+                     is NSNull,
+                     _? /* any other unrelated type */ :
+                    return nil
+                }
+            }
+            self.setPrimitiveValue = {
+
+                rawObject.setPrimitiveValue(
+                    $0,
+                    forKey: keyPathString
+                )
+            }
+        }
+
+        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Coded<V>) {
+
+            let keyPathString = field.keyPath
+            self.getValue = {
+
+                return FieldContainer<O>.Coded<V>.read(field: field, for: rawObject) as! V
+            }
+            self.setValue = {
+
+                FieldContainer<O>.Coded<V>.modify(field: field, for: rawObject, newValue: $0)
+            }
+            self.getPrimitiveValue = {
+
+                switch rawObject.primitiveValue(forKey: keyPathString) {
+
+                case let valueBox as Internals.AnyFieldCoder.TransformableDefaultValueCodingBox:
+                    rawObject.setPrimitiveValue(valueBox.value, forKey: keyPathString)
+                    return valueBox.value as? V
+
+                case let value as V:
+                    return value
+
+                case nil,
+                     is NSNull,
+                      _? /* any other unrelated type */ :
+                     return nil
+                }
+            }
+            self.setPrimitiveValue = {
+
+                rawObject.setPrimitiveValue(
+                    $0,
+                    forKey: keyPathString
+                )
+            }
+        }
+
+
+        // MARK: Private
+
+        private let getValue: () -> V
+        private let setValue: (V) -> Void
+        private let getPrimitiveValue: () -> V?
+        private let setPrimitiveValue: (V?) -> Void
+    }
+}