From 0a8f154ab2ba50c4649bcc03d5e7d0a038bda6e0 Mon Sep 17 00:00:00 2001
From: Matthew Johnson <matthew@anandabits.com>
Date: Tue, 9 Jul 2019 10:14:34 -0500
Subject: [PATCH] Add Identifiable protocol to the standard library

---
 stdlib/public/core/CMakeLists.txt     |  1 +
 stdlib/public/core/GroupInfo.json     |  1 +
 stdlib/public/core/Identifiable.swift | 29 +++++++++++++++++++++++++++
 test/stdlib/Identifiable.swift        |  7 +++++++
 4 files changed, 38 insertions(+)
 create mode 100644 stdlib/public/core/Identifiable.swift
 create mode 100644 test/stdlib/Identifiable.swift

diff --git a/stdlib/public/core/CMakeLists.txt b/stdlib/public/core/CMakeLists.txt
index ecb5a5a0743a6..a86190606b585 100644
--- a/stdlib/public/core/CMakeLists.txt
+++ b/stdlib/public/core/CMakeLists.txt
@@ -75,6 +75,7 @@ set(SWIFTLIB_ESSENTIAL
   Hashing.swift
   HashTable.swift
   ICU.swift
+  Identifiable.swift
   Indices.swift
   InputStream.swift
   IntegerParsing.swift
diff --git a/stdlib/public/core/GroupInfo.json b/stdlib/public/core/GroupInfo.json
index a09e00d5c39c3..15a1c7f6e59e6 100644
--- a/stdlib/public/core/GroupInfo.json
+++ b/stdlib/public/core/GroupInfo.json
@@ -199,6 +199,7 @@
   "Misc": [
     "AtomicInt.swift",
     "ErrorType.swift",
+    "Identifiable.swift",
     "InputStream.swift",
     "LifetimeManager.swift",
     "ManagedBuffer.swift",
diff --git a/stdlib/public/core/Identifiable.swift b/stdlib/public/core/Identifiable.swift
new file mode 100644
index 0000000000000..c9a9147abf8c8
--- /dev/null
+++ b/stdlib/public/core/Identifiable.swift
@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2019 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// A class of types whose instances hold the value of an entity with stable identity.
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+public protocol Identifiable {
+
+  /// A type representing the stable identity of the entity associated with `self`.
+  associatedtype ID: Hashable
+
+  /// The stable identity of the entity associated with `self`.
+  var id: ID { get }
+}
+
+@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
+extension Identifiable where Self: AnyObject {
+  public var id: ObjectIdentifier {
+    return ObjectIdentifier(self)
+  }
+}
diff --git a/test/stdlib/Identifiable.swift b/test/stdlib/Identifiable.swift
new file mode 100644
index 0000000000000..a801356424574
--- /dev/null
+++ b/test/stdlib/Identifiable.swift
@@ -0,0 +1,7 @@
+// RUN: %target-typecheck-verify-swift
+
+struct IdentifiableValue: Identifiable {
+  let id = 42
+}
+
+class IdentifiableClass: Identifiable {}
\ No newline at end of file