Add IdentityEquatable and IdentityHashable

Sources/ReactorKit/IdentityEquatable.swift

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+//
+//  IdentityEquatable.swift
+//  ReactorKit
+//
+//  Created by Suyeol Jeon on 2019/10/17.
+//
+
+public protocol IdentityEquatable: class, Equatable {
+}
+
+public extension IdentityEquatable {
+  static func == (lhs: Self, rhs: Self) -> Bool {
+    return lhs === rhs
+  }
+}

Sources/ReactorKit/IdentityHashable.swift

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+//
+//  IdentityHashable.swift
+//  ReactorKit
+//
+//  Created by Suyeol Jeon on 2019/10/17.
+//
+
+public protocol IdentityHashable: Hashable, IdentityEquatable {
+}
+
+public extension IdentityHashable {
+  func hash(into hasher: inout Hasher) {
+    hasher.combine(ObjectIdentifier(self).hashValue)
+  }
+}

Tests/ReactorKitTests/IdentityEquatableTests.swift

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+//
+//  IdentityEquatableTests.swift
+//  ReactorKitTests
+//
+//  Created by Suyeol Jeon on 2019/10/17.
+//
+
+import XCTest
+import ReactorKit
+import RxSwift
+
+final class IdentityEquatableTests: XCTestCase {
+  func testReactorEqual_whenCurrentStatesAreEqual() {
+    let reactorA = SimpleReactor()
+    let reactorB = reactorA
+    XCTAssertEqual(reactorA, reactorB)
+  }
+}
+
+private final class SimpleReactor: Reactor, IdentityEquatable {
+  typealias Action = Never
+  typealias Mutation = Never
+  struct State {
+  }
+
+  let initialState = State()
+}

Tests/ReactorKitTests/IdentityHashableTests.swift

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+//
+//  IdentityHashableTests.swift
+//  ReactorKitTests
+//
+//  Created by Suyeol Jeon on 2019/10/17.
+//
+
+import XCTest
+import ReactorKit
+import RxSwift
+
+final class IdentityHashableTests: XCTestCase {
+  func testReactorHashValue() {
+    let reactorA = SimpleReactor()
+    let reactorB = reactorA
+    XCTAssertEqual(reactorA.hashValue, reactorB.hashValue)
+    XCTAssertEqual(reactorA, reactorB)
+  }
+}
+
+private final class SimpleReactor: Reactor, IdentityHashable {
+  typealias Action = Never
+  typealias Mutation = Never
+  struct State {
+  }
+
+  let initialState = State()
+}