robtimp · June 26, 2019 17:02 · Jun 26, 2019
diff --git a/CircularEnum.swift b/CircularEnum.swift
@@ -0,0 +1,43 @@
+protocol CircularEnum: CaseIterable where Self.AllCases.Element: Equatable {
+    var currentIndex: Self.AllCases.Index { get }
+    func next() -> Self.AllCases.Element
+    func previous() -> Self.AllCases.Element
+}
+
+extension CircularEnum {
+    var currentIndex: Self.AllCases.Index {
+        return Self.allCases.firstIndex(of: self)!
+    }
+
+    func next() -> Self.AllCases.Element {
+        let allCases = Self.allCases
+        let nextIndex = allCases.index(after: currentIndex)
+        if nextIndex == allCases.endIndex {
+            return allCases.first!
+        }
+
+        return allCases[nextIndex]
+    }
+
+    func previous() -> Self.AllCases.Element {
+        let allCases = Self.allCases
+        var index = currentIndex
+        if index == allCases.startIndex {
+            index = allCases.endIndex
+        }
+        index = allCases.index(index, offsetBy: -1)
+
+        return allCases[index]
+    }
+}
+
+enum Season: CircularEnum {
+    case winter
+    case spring
+    case summer
+    case fall
+}
+
+let season = Season.fall
+season.previous() // summer
+season.next() // winter
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