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Sources/Internals.LazyNonmutating.swift

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+//
+//  Internals.LazyNonmutating.swift
+//  CoreStore
+//
+//  Copyright © 2018 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 Foundation
+
+
+// MARK: - Internals
+
+extension Internals {
+
+    // MARK: - LazyNonmutating
+
+    @propertyWrapper
+    internal final class LazyNonmutating<Value> {
+
+        // MARK: Internal
+
+        init(_ initializer: @escaping () -> Value) {
+
+            self.initializer = initializer
+        }
+
+        init(uninitialized: Void) {
+
+            self.initializer = { fatalError() }
+        }
+
+        func initialize(_ initializer: @escaping () -> Value) {
+
+            self.initializer = initializer
+        }
+
+        func reset(_ initializer: @escaping () -> Value) {
+
+            self.initializer = initializer
+            self.initializedValue = nil
+        }
+
+
+        // MARK: @propertyWrapper
+
+        var wrappedValue: Value {
+
+            get {
+
+                if let initializedValue = self.initializedValue {
+
+                    return initializedValue
+                }
+                let initializedValue = self.initializer()
+                self.initializedValue = initializedValue
+                return initializedValue
+            }
+            set {
+
+                self.initializer = { newValue }
+                self.initializedValue = newValue
+            }
+        }
+
+        var projectedValue: Internals.LazyNonmutating<Value> {
+
+            return self
+        }
+
+
+        // MARK: Private
+
+        private var initializer: () -> Value
+        private var initializedValue: Value? = nil
+    }
+}