CoreStore/Sources/Field.Stored.swift

//
//  Field.Stored.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: - FieldContainer

extension FieldContainer {

    // MARK: - Stored

    /**
     The containing type for stored property values. Any type that conforms to `FieldStorableType` are supported.
     ```
     class Person: CoreStoreObject {

         @Field.Stored("title")
         var title: String = "Mr."

         @Field.Stored("nickname")
         var nickname: String?
     }
     ```
     - Important: `Field` properties are required to be used as `@propertyWrapper`s. Any other declaration not using the `@Field.Stored(...) var` syntax will be ignored.     
     */
    @propertyWrapper
    public struct Stored<V: FieldStorableType>: AttributeKeyPathStringConvertible, FieldAttributeProtocol {

#if swift(<5.4)

        /**
         Initializes the metadata for the property.
         ```
         class Person: CoreStoreObject {

             @Field.Stored("title")
             var title: String = "Mr."
         }
         ```
         - parameter initial: the initial value for the property that is shared for all instances of this object. Note that this is evaluated during `DataStack` setup, not during object creation. To assign a value during object creation, use the `dynamicInitialValue` argument instead.
         - parameter keyPath: the permanent attribute name for this property.
         - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
         - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
         - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
         - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
         - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
         */
        public init(
            wrappedValue initial: @autoclosure @escaping () -> V,
            _ keyPath: KeyPathString = { fatalError("'keyPath' argument required (SR-13069 workaround)") }(),
            versionHashModifier: @autoclosure @escaping () -> String? = nil,
            previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
            customGetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>) -> V)? = nil,
            customSetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>, _ newValue: V) -> Void)? = nil,
            affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = []
        ) {

            self.init(
                wrappedValue: initial,
                keyPath: keyPath,
                isOptional: false,
                versionHashModifier: versionHashModifier,
                renamingIdentifier: previousVersionKeyPath,
                customGetter: customGetter,
                customSetter: customSetter,
                dynamicInitialValue: nil,
                affectedByKeyPaths: affectedByKeyPaths
            )
        }

#else

      /**
       Initializes the metadata for the property.
       ```
       class Person: CoreStoreObject {

           @Field.Stored("title")
           var title: String = "Mr."
       }
       ```
       - parameter initial: the initial value for the property that is shared for all instances of this object. Note that this is evaluated during `DataStack` setup, not during object creation. To assign a value during object creation, use the `dynamicInitialValue` argument instead.
       - parameter keyPath: the permanent attribute name for this property.
       - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
       - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
       - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
       - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
       - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
       */
      public init(
          wrappedValue initial: @autoclosure @escaping () -> V,
          _ keyPath: KeyPathString,
          versionHashModifier: @autoclosure @escaping () -> String? = nil,
          previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
          customGetter: (
            (
                _ object: ObjectProxy<O>,
                _ field: ObjectProxy<O>.FieldProxy<V>
            ) -> V
          )? = nil,
          customSetter: (
            (
                _ object: ObjectProxy<O>,
                _ field: ObjectProxy<O>.FieldProxy<V>,
                _ newValue: V
            ) -> Void
          )? = nil,
          affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = []
      ) {

          self.init(
              wrappedValue: initial,
              keyPath: keyPath,
              isOptional: false,
              versionHashModifier: versionHashModifier,
              renamingIdentifier: previousVersionKeyPath,
              customGetter: customGetter,
              customSetter: customSetter,
              dynamicInitialValue: nil,
              affectedByKeyPaths: affectedByKeyPaths
          )
      }

#endif
        
        /**
         Initializes the metadata for the property.
         ```
         class Person: CoreStoreObject {

             @Field.Stored("title", dynamicInitialValue: { Person.randomTitle() })
             var title: String
         }
         ```
         - parameter keyPath: the permanent attribute name for this property.
         - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
         - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
         - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
         - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
         - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
         - parameter dynamicInitialValue: the initial value for the property when the object is first created.
         */
        public init(
            _ keyPath: KeyPathString,
            versionHashModifier: @autoclosure @escaping () -> String? = nil,
            previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
            customGetter: (
                (
                    _ object: ObjectProxy<O>,
                    _ field: ObjectProxy<O>.FieldProxy<V>
                ) -> V
            )? = nil,
            customSetter: (
                (
                    _ object: ObjectProxy<O>,
                    _ field: ObjectProxy<O>.FieldProxy<V>,
                    _ newValue: V
                ) -> Void
            )? = nil,
            affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = [],
            dynamicInitialValue: @escaping () -> V
        ) {

            self.init(
                wrappedValue: nil,
                keyPath: keyPath,
                isOptional: false,
                versionHashModifier: versionHashModifier,
                renamingIdentifier: previousVersionKeyPath,
                customGetter: customGetter,
                customSetter: customSetter,
                dynamicInitialValue: dynamicInitialValue,
                affectedByKeyPaths: affectedByKeyPaths
            )
        }


        // MARK: @propertyWrapper

        @available(*, unavailable)
        public var wrappedValue: V {

            get { fatalError() }
            set { fatalError() }
        }

        public var projectedValue: Self {

            return self
        }

        public static subscript(
            _enclosingInstance instance: O,
            wrapped wrappedKeyPath: ReferenceWritableKeyPath<O, V>,
            storage storageKeyPath: ReferenceWritableKeyPath<O, Self>
        ) -> V {

            get {

                Internals.assert(
                    instance.rawObject != nil,
                    "Attempted to access values from a \(Internals.typeName(O.self)) meta object. Meta objects are only used for querying keyPaths and infering types."
                )
                Internals.assert(
                    instance.rawObject?.isRunningInAllowedQueue() == true,
                    "Attempted to access \(Internals.typeName(O.self))'s value outside it's designated queue."
                )
                return self.read(field: instance[keyPath: storageKeyPath], for: instance.rawObject!) as! V
            }
            set {

                Internals.assert(
                    instance.rawObject != nil,
                    "Attempted to access values from a \(Internals.typeName(O.self)) meta object. Meta objects are only used for querying keyPaths and infering types."
                )
                Internals.assert(
                    instance.rawObject?.isRunningInAllowedQueue() == true,
                    "Attempted to access \(Internals.typeName(O.self))'s value outside it's designated queue."
                )
                return self.modify(field: instance[keyPath: storageKeyPath], for: instance.rawObject!, newValue: newValue)
            }
        }


        // MARK: AnyKeyPathStringConvertible

        public var cs_keyPathString: String {

            return self.keyPath
        }


        // MARK: KeyPathStringConvertible

        public typealias ObjectType = O
        public typealias DestinationValueType = V


        // MARK: AttributeKeyPathStringConvertible

        public typealias ReturnValueType = DestinationValueType


        // MARK: PropertyProtocol

        internal let keyPath: KeyPathString


        // MARK: FieldProtocol

        internal static var dynamicObjectType: CoreStoreObject.Type {

            return ObjectType.self
        }

        internal static func read(
            field: FieldProtocol,
            for rawObject: CoreStoreManagedObject
        ) -> Any? {

            let field = field as! Self
            if let customGetter = field.customGetter {

                return customGetter(
                    ObjectProxy<O>(rawObject),
                    ObjectProxy<O>.FieldProxy<V>(rawObject: rawObject, field: field)
                )
            }
            let keyPath = field.keyPath
            switch rawObject.value(forKey: keyPath) {

            case let rawValue as V.FieldStoredNativeType:
                return V.cs_fromFieldStoredNativeType(rawValue)

            default:
                return nil
            }
        }

        internal static func modify(
            field: FieldProtocol,
            for rawObject: CoreStoreManagedObject, newValue: Any?
        ) {

            Internals.assert(
                rawObject.isEditableInContext() == true,
                "Attempted to update a \(Internals.typeName(O.self))'s value from outside a transaction."
            )
            let newValue = newValue as! V
            let field = field as! Self
            let keyPath = field.keyPath
            if let customSetter = field.customSetter {

                return customSetter(
                    ObjectProxy<O>(rawObject),
                    ObjectProxy<O>.FieldProxy<V>(rawObject: rawObject, field: field),
                    newValue
                )
            }
            return rawObject.setValue(
                newValue.cs_toFieldStoredNativeType(),
                forKey: keyPath
            )
        }


        // MARK: FieldAttributeProtocol

        internal let entityDescriptionValues: () -> FieldAttributeProtocol.EntityDescriptionValues

        internal var getter: CoreStoreManagedObject.CustomGetter? {

            guard let customGetter = self.customGetter else {

                return nil
            }
            let keyPath = self.keyPath
            return { (_ id: Any) -> Any? in

                let rawObject = id as! CoreStoreManagedObject
                rawObject.willAccessValue(forKey: keyPath)
                defer {

                    rawObject.didAccessValue(forKey: keyPath)
                }
                let value = customGetter(
                    ObjectProxy<O>(rawObject),
                    ObjectProxy<O>.FieldProxy<V>(rawObject: rawObject, field: self)
                )
                return value.cs_toFieldStoredNativeType()
            }
        }

        internal var setter: CoreStoreManagedObject.CustomSetter? {

            guard let customSetter = self.customSetter else {

                return nil
            }
            let keyPath = self.keyPath
            return { (_ id: Any, _ newValue: Any?) -> Void in

                let rawObject = id as! CoreStoreManagedObject
                rawObject.willChangeValue(forKey: keyPath)
                defer {

                    rawObject.didChangeValue(forKey: keyPath)
                }
                customSetter(
                    ObjectProxy<O>(rawObject),
                    ObjectProxy<O>.FieldProxy<V>(rawObject: rawObject, field: self),
                    V.cs_fromFieldStoredNativeType(newValue as! V.FieldStoredNativeType)
                )
            }
        }
        
        internal var initializer: CoreStoreManagedObject.CustomInitializer? {
            
            guard let dynamicInitialValue = self.dynamicInitialValue else {
                
                return nil
            }
            let keyPath = self.keyPath
            return { (_ id: Any) -> Void in
                
                let rawObject = id as! CoreStoreManagedObject
                rawObject.setPrimitiveValue(
                    dynamicInitialValue().cs_toFieldStoredNativeType(),
                    forKey: keyPath
                )
            }
        }


        // MARK: FilePrivate

        fileprivate init(
            wrappedValue initial: (() -> V)?,
            keyPath: KeyPathString,
            isOptional: Bool,
            versionHashModifier: @escaping () -> String?,
            renamingIdentifier: @escaping () -> String?,
            customGetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>) -> V)?,
            customSetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>, _ newValue: V) -> Void)?,
            dynamicInitialValue: (() -> V)?,
            affectedByKeyPaths: @escaping () -> Set<KeyPathString>
        ) {

            self.keyPath = keyPath
            self.entityDescriptionValues = {
                (
                    attributeType: V.cs_rawAttributeType,
                    isOptional: isOptional,
                    isTransient: false,
                    allowsExternalBinaryDataStorage: false,
                    versionHashModifier: versionHashModifier(),
                    renamingIdentifier: renamingIdentifier(),
                    valueTransformer: nil,
                    affectedByKeyPaths: affectedByKeyPaths(),
                    defaultValue: initial?().cs_toFieldStoredNativeType()
                )
            }
            self.customGetter = customGetter
            self.customSetter = customSetter
            self.dynamicInitialValue = dynamicInitialValue
        }


        // MARK: Private

        private let customGetter: (
            (
                _ object: ObjectProxy<O>,
                _ field: ObjectProxy<O>.FieldProxy<V>
            ) -> V
        )?
        private let customSetter: (
            (
                _ object: ObjectProxy<O>,
                _ field: ObjectProxy<O>.FieldProxy<V>,
                _ newValue: V
            ) -> Void
        )?
        private let dynamicInitialValue: (() -> V)?
    }
}


// MARK: - FieldContainer.Stored where V: FieldOptionalType

extension FieldContainer.Stored where V: FieldOptionalType {

#if swift(<5.4)

    /**
     Initializes the metadata for the property.
     ```
     class Person: CoreStoreObject {

         @Field.Stored("nickname")
         var nickname: String?
     }
     ```
     - parameter initial: the initial value for the property that is shared for all instances of this object. Note that this is evaluated during `DataStack` setup, not during object creation. To assign a value during object creation, use the `dynamicInitialValue` argument instead.     
     - parameter keyPath: the permanent attribute name for this property.
     - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
     - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
     - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
     - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
     - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
     */
    public init(
        wrappedValue initial: @autoclosure @escaping () -> V = nil,
        _ keyPath: KeyPathString = { fatalError("'keyPath' argument required (SR-13069 workaround)") }(),
        versionHashModifier: @autoclosure @escaping () -> String? = nil,
        previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
        customGetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>) -> V)? = nil,
        customSetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>, _ newValue: V) -> Void)? = nil,
        affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = []
    ) {

        self.init(
            wrappedValue: initial,
            keyPath: keyPath,
            isOptional: true,
            versionHashModifier: versionHashModifier,
            renamingIdentifier: previousVersionKeyPath,
            customGetter: customGetter,
            customSetter: customSetter,
            dynamicInitialValue: nil,
            affectedByKeyPaths: affectedByKeyPaths
        )
    }

#else

    /**
     Initializes the metadata for the property.
     ```
     class Person: CoreStoreObject {

         @Field.Stored("nickname")
         var nickname: String?
     }
     ```
     - parameter initial: the initial value for the property that is shared for all instances of this object. Note that this is evaluated during `DataStack` setup, not during object creation. To assign a value during object creation, use the `dynamicInitialValue` argument instead.
     - parameter keyPath: the permanent attribute name for this property.
     - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
     - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
     - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
     - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
     - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
     */
    public init(
        wrappedValue initial: @autoclosure @escaping () -> V = nil,
        _ keyPath: KeyPathString = { fatalError("'keyPath' argument required (SR-13069 workaround)") }(),
        versionHashModifier: @autoclosure @escaping () -> String? = nil,
        previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
        customGetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>) -> V)? = nil,
        customSetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>, _ newValue: V) -> Void)? = nil,
        affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = []
    ) {

        self.init(
            wrappedValue: initial,
            keyPath: keyPath,
            isOptional: true,
            versionHashModifier: versionHashModifier,
            renamingIdentifier: previousVersionKeyPath,
            customGetter: customGetter,
            customSetter: customSetter,
            dynamicInitialValue: nil,
            affectedByKeyPaths: affectedByKeyPaths
        )
    }

#endif
    
    /**
     Initializes the metadata for the property.
     ```
     class Person: CoreStoreObject {

         @Field.Stored("nickname", dynamicInitialValue: { Person.randomNickname() })
         var nickname: String?
     }
     ```
     - parameter keyPath: the permanent attribute name for this property.
     - parameter versionHashModifier: used to mark or denote a property as being a different "version" than another even if all of the values which affect persistence are equal. (Such a difference is important in cases where the properties are unchanged but the format or content of its data are changed.)
     - parameter previousVersionKeyPath: used to resolve naming conflicts between models. When creating an entity mapping between entities in two managed object models, a source entity property's `keyPath` with a matching destination entity property's `previousVersionKeyPath` indicate that a property mapping should be configured to migrate from the source to the destination. If unset, the identifier will be the property's `keyPath`.
     - parameter customGetter: use this closure as an "override" for the default property getter. The closure receives a `ObjectProxy<O>`, which acts as a type-safe proxy for the receiver. When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively. Do not make assumptions on the thread/queue that the closure is executed on; accessors may be called from `NSError` logs for example.
     - parameter customSetter: use this closure as an "override" for the default property setter. The closure receives a `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 everytime KVO invokes this accessor method incurs a cumulative performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `field.primitiveValue` instead of `field.value`, which would unintentionally execute the same closure again recursively.
     - parameter affectedByKeyPaths: a set of key paths for properties whose values affect the value of the receiver. This is similar to `NSManagedObject.keyPathsForValuesAffectingValue(forKey:)`.
     - parameter dynamicInitialValue: the initial value for the property when the object is first created.
     */
    public init(
        _ keyPath: KeyPathString,
        versionHashModifier: @autoclosure @escaping () -> String? = nil,
        previousVersionKeyPath: @autoclosure @escaping () -> String? = nil,
        customGetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>) -> V)? = nil,
        customSetter: ((_ object: ObjectProxy<O>, _ field: ObjectProxy<O>.FieldProxy<V>, _ newValue: V) -> Void)? = nil,
        affectedByKeyPaths: @autoclosure @escaping () -> Set<KeyPathString> = [],
        dynamicInitialValue: @escaping () -> V
    ) {

        self.init(
            wrappedValue: nil,
            keyPath: keyPath,
            isOptional: true,
            versionHashModifier: versionHashModifier,
            renamingIdentifier: previousVersionKeyPath,
            customGetter: customGetter,
            customSetter: customSetter,
            dynamicInitialValue: dynamicInitialValue,
            affectedByKeyPaths: affectedByKeyPaths
        )
    }
}