wip

0230-composable-navigation-pt9/Inventory/COW.playground/Contents.swift

@@ -0,0 +1,62 @@
+
+struct Wrapper<Value> {
+  var value: Value {
+    get { self.storage.value }
+    set {
+      if Swift.isKnownUniquelyReferenced(&self.storage) {
+        self.storage.value = newValue
+      } else {
+        self.storage = Storage(value: newValue)
+      }
+    }
+  }
+
+  private var storage: Storage
+
+  init(value: Value) {
+    self.storage = Storage(value: value)
+  }
+
+  mutating func isKnownUniquelyReferenced() -> Bool {
+    Swift.isKnownUniquelyReferenced(&self.storage)
+  }
+
+  private class Storage {
+    var value: Value
+    init(value: Value) {
+      self.value = value
+    }
+  }
+}
+
+import Foundation
+
+extension Wrapper: Equatable where Value: Equatable {
+  static func == (lhs: Self, rhs: Self) -> Bool {
+    if lhs.storage === rhs.storage {
+      return true
+    }
+    Thread.sleep(forTimeInterval: 3)
+    return lhs.value == rhs.value
+  }
+}
+
+var x = Wrapper(value: 1)
+x.isKnownUniquelyReferenced()
+var y = x
+x.isKnownUniquelyReferenced()
+y.isKnownUniquelyReferenced()
+x == y
+x.value = 2
+y.value = 2
+x == y
+y.value
+x.value
+x.isKnownUniquelyReferenced()
+y.isKnownUniquelyReferenced()
+
+var z = 1
+var w = z
+z = 2
+w
+z

0230-composable-navigation-pt9/Inventory/COW.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>