Parameter Packs in onChange

Sources/SwiftUISupport/Extensions/OnChange.swift

@@ -0,0 +1,112 @@
+import SwiftUI
+
+extension View {
+
+  public func onChange<each T: Equatable>(each value: repeat each T, action: @escaping () -> Void)
+  -> some View
+  {
+
+    if #available(iOS 17, *) {
+
+      let box = RepeatingBox<repeat each T>(value: (repeat each value))
+
+      return self.onChange(
+        of: box,
+        perform: { _ in
+          action()
+        })
+
+    } else {
+
+      let box = TupleBox<(repeat each T)>(
+        value: (repeat each value),
+        isEqual: { lhs, rhs in
+
+          for (left, right) in repeat (each lhs, each rhs) {
+            guard left == right else { return false }
+          }
+          return true
+
+        })
+
+      return self.onChange(
+        of: box,
+        perform: { _ in
+          action()
+        })
+    }
+
+  }
+
+}
+
+private struct TupleBox<T>: Equatable {
+
+  static func == (lhs: TupleBox<T>, rhs: TupleBox<T>) -> Bool {
+    lhs.isEqual(lhs.value, rhs.value)
+  }
+
+  let value: T
+  let isEqual: (T, T) -> Bool
+
+  init(
+    value: T,
+    isEqual: @escaping (T, T) -> Bool
+  ) {
+    self.value = value
+    self.isEqual = isEqual
+  }
+
+}
+
+@available(iOS 17.0.0, *)
+private struct RepeatingBox<each T: Equatable>: Equatable {
+
+  static func == (lhs: Self, rhs: Self) -> Bool {
+    for (left, right) in repeat (each lhs.value, each rhs.value) {
+      guard left == right else { return false }
+    }
+    return true
+  }
+
+  let value: (repeat each T)
+
+}
+
+#if DEBUG
+
+private struct Book: View {
+
+  @State var a: Int = 0
+  @State var b: Int = 0
+  @State var c: Int = 0
+
+  var body: some View {
+
+    VStack {
+
+      Button("Increment A") {
+        a += 1
+      }
+      Button("Increment B") {
+        b += 1
+      }
+      Button("Increment C") {
+        c += 1
+
+      }
+      .onChange(each: a, b, c) {
+        print("a, b, or c changed")
+      }
+
+    }
+
+  }
+
+}
+
+#Preview {
+  Book()
+}
+
+#endif