Add implementation of shuffle on IdentifiedArray (#254)

* add shuffle

* Update Tests/ComposableArchitectureTests/IdentifiedArrayTests.swift

* Update IdentifiedArrayTests.swift

Co-authored-by: Stephen Celis <stephen.celis@gmail.com>

Sources/ComposableArchitecture/SwiftUI/IdentifiedArray.swift

@@ -190,6 +190,15 @@ where ID: Hashable {
       try areInIncreasingOrder(self.dictionary[$0]!, self.dictionary[$1]!)
     }
   }
+  
+  public mutating func shuffle<T>(using generator: inout T) where T : RandomNumberGenerator {
+    ids.shuffle(using: &generator)
+  }
+  
+  public mutating func shuffle() {
+    var rng = SystemRandomNumberGenerator()
+    self.shuffle(using: &rng)
+  }
 }
 
 extension IdentifiedArray: CustomDebugStringConvertible {

Tests/ComposableArchitectureTests/IdentifiedArrayTests.swift

@@ -195,4 +195,36 @@ final class IdentifiedArrayTests: XCTestCase {
       ], array)
 
   }
+  
+  // Account for randomness API changes in Swift 5.3 (https://twitter.com/mbrandonw/status/1262388756847505410)
+  // TODO: Try swapping out the LCRNG for a Xoshiro generator
+  #if swift(>=5.3)
+  func testShuffle() {
+    struct User: Equatable, Identifiable {
+      let id: Int
+      var name: String
+    }
+
+    var array: IdentifiedArray = [
+      User(id: 1, name: "Blob"),
+      User(id: 2, name: "Blob Jr."),
+      User(id: 3, name: "Blob Sr."),
+      User(id: 4, name: "Foo Jr."),
+      User(id: 5, name: "Bar Jr."),
+    ]
+    var lcrng = LCRNG(seed: 0)
+    array.shuffle(using: &lcrng)
+    XCTAssertEqual(
+      [
+        User(id: 1, name: "Blob"),
+        User(id: 3, name: "Blob Sr."),
+        User(id: 5, name: "Bar Jr."),
+        User(id: 4, name: "Foo Jr."),
+        User(id: 2, name: "Blob Jr.")
+      ],
+      array.elements
+    )
+    XCTAssertEqual([1, 3, 5, 4, 2], array.ids)
+  }
+  #endif
 }

Tests/ComposableArchitectureTests/LCRNG.swift

@@ -0,0 +1,15 @@
+/// A linear congruential random number generator.
+public struct LCRNG: RandomNumberGenerator {
+  public var seed: UInt64
+
+  @inlinable
+  public init(seed: UInt64) {
+    self.seed = seed
+  }
+
+  @inlinable
+  public mutating func next() -> UInt64 {
+    seed = 2862933555777941757 &* seed &+ 3037000493
+    return seed
+  }
+}