[stdlib] array identical

Co-Authored-By: Ben Rimmington <me@benrimmington.com>

Author: vanvoorden

benchmark/CMakeLists.txt

@@ -39,7 +39,9 @@ set(SWIFT_BENCH_MODULES
     single-source/ArrayOfRef
     single-source/ArrayRemoveAll
     single-source/ArraySetElement
+    single-source/ArraySliceTests
     single-source/ArraySubscript
+    single-source/ArrayTests
     single-source/AsyncTree
     single-source/BinaryFloatingPointConversionFromBinaryInteger
     single-source/BinaryFloatingPointProperties
@@ -65,6 +67,7 @@ set(SWIFT_BENCH_MODULES
     single-source/ClassArrayGetter
     single-source/CodableTest
     single-source/Combos
+    single-source/ContiguousArrayTests
     single-source/CountAlgo
     single-source/DataBenchmarks
     single-source/DeadArray

benchmark/single-source/ArraySliceTests.swift

@@ -0,0 +1,46 @@
+//===--- ArraySliceTests.swift --------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 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
+//
+//===----------------------------------------------------------------------===//
+
+import TestsUtils
+
+public let benchmarks = [
+  BenchmarkInfo(name: "ArraySliceEqualUnique", runFunction: run_ArraySliceEqualUnique, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ArraySliceEqualShared", runFunction: run_ArraySliceEqualShared, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ArraySliceIdentical", runFunction: run_ArraySliceIdentical, tags: [.validation, .api, .Array]),
+]
+
+@inline(never)
+public func run_ArraySliceEqualUnique(_ n: Int) {
+  let a1 = ArraySlice(0 ..< n)
+  let a2 = ArraySlice(0 ..< n)
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ArraySliceEqualShared(_ n: Int) {
+  let a1 = ArraySlice(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ArraySliceIdentical(_ n: Int) {
+  let a1 = ArraySlice(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1.isTriviallyIdentical(to: a2))
+  }
+}

benchmark/single-source/ArrayTests.swift

@@ -0,0 +1,46 @@
+//===--- ArrayTests.swift -------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 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
+//
+//===----------------------------------------------------------------------===//
+
+import TestsUtils
+
+public let benchmarks = [
+  BenchmarkInfo(name: "ArrayEqualUnique", runFunction: run_ArrayEqualUnique, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ArrayEqualShared", runFunction: run_ArrayEqualShared, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ArrayIdentical", runFunction: run_ArrayIdentical, tags: [.validation, .api, .Array]),
+]
+
+@inline(never)
+public func run_ArrayEqualUnique(_ n: Int) {
+  let a1 = Array(0 ..< n)
+  let a2 = Array(0 ..< n)
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ArrayEqualShared(_ n: Int) {
+  let a1 = Array(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ArrayIdentical(_ n: Int) {
+  let a1 = Array(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1.isTriviallyIdentical(to: a2))
+  }
+}

benchmark/single-source/ContiguousArrayTests.swift

@@ -0,0 +1,46 @@
+//===--- ContiguousArrayTests.swift ---------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 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
+//
+//===----------------------------------------------------------------------===//
+
+import TestsUtils
+
+public let benchmarks = [
+  BenchmarkInfo(name: "ContiguousArrayEqualUnique", runFunction: run_ContiguousArrayEqualUnique, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ContiguousArrayEqualShared", runFunction: run_ContiguousArrayEqualShared, tags: [.validation, .api, .Array]),
+  BenchmarkInfo(name: "ContiguousArrayIdentical", runFunction: run_ContiguousArrayIdentical, tags: [.validation, .api, .Array]),
+]
+
+@inline(never)
+public func run_ContiguousArrayEqualUnique(_ n: Int) {
+  let a1 = ContiguousArray(0 ..< n)
+  let a2 = ContiguousArray(0 ..< n)
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ContiguousArrayEqualShared(_ n: Int) {
+  let a1 = ContiguousArray(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1 == a2)
+  }
+}
+
+@inline(never)
+public func run_ContiguousArrayIdentical(_ n: Int) {
+  let a1 = ContiguousArray(0 ..< n)
+  let a2 = a1
+  for _ in 0 ..< 100_000 {
+    check(a1.isTriviallyIdentical(to: a2))
+  }
+}

benchmark/utils/main.swift

@@ -27,7 +27,9 @@ import ArrayOfPOD
 import ArrayOfRef
 import ArrayRemoveAll
 import ArraySetElement
+import ArraySliceTests
 import ArraySubscript
+import ArrayTests
 import AsyncTree
 import BinaryFloatingPointConversionFromBinaryInteger
 import BinaryFloatingPointProperties
@@ -53,6 +55,7 @@ import Chars
 import ClassArrayGetter
 import CodableTest
 import Combos
+import ContiguousArrayTests
 import CountAlgo
 import CreateObjects
 // rdar://128520766
@@ -229,7 +232,9 @@ register(ArrayOfPOD.benchmarks)
 register(ArrayOfRef.benchmarks)
 register(ArrayRemoveAll.benchmarks)
 register(ArraySetElement.benchmarks)
+register(ArraySliceTests.benchmarks)
 register(ArraySubscript.benchmarks)
+register(ArrayTests.benchmarks)
 register(AsyncTree.benchmarks)
 register(BinaryFloatingPointConversionFromBinaryInteger.benchmarks)
 register(BinaryFloatingPointProperties.benchmarks)
@@ -254,6 +259,7 @@ register(CharacterRecognizer.benchmarks)
 register(Chars.benchmarks)
 register(CodableTest.benchmarks)
 register(Combos.benchmarks)
+register(ContiguousArrayTests.benchmarks)
 register(CountAlgo.benchmarks)
 register(ClassArrayGetter.benchmarks)
 register(CreateObjects.benchmarks)

stdlib/public/core/Array.swift

@@ -2160,3 +2160,44 @@ internal struct _ArrayAnyHashableBox<Element: Hashable>
 }
 
 extension Array: @unchecked Sendable where Element: Sendable { }
+
+extension Array {
+  /// Returns a boolean value indicating whether this array is identical to
+  /// `other`.
+  ///
+  /// Two array values are identical if there is no way to distinguish between
+  /// them.
+  /// 
+  /// For any values `a`, `b`, and `c`:
+  ///
+  /// - `a.isTriviallyIdentical(to: a)` is always `true`. (Reflexivity)
+  /// - `a.isTriviallyIdentical(to: b)` implies `b.isTriviallyIdentical(to: a)`.
+  /// (Symmetry)
+  /// - If `a.isTriviallyIdentical(to: b)` and `b.isTriviallyIdentical(to: c)`
+  /// are both `true`, then `a.isTriviallyIdentical(to: c)` is also `true`.
+  /// (Transitivity)
+  /// - If `a` and `b` are `Equatable`, then `a.isTriviallyIdentical(b)` implies
+  /// `a == b`
+  ///   - `a == b` does not imply `a.isTriviallyIdentical(b)`
+  ///
+  /// Values produced by copying the same value, with no intervening mutations,
+  /// will compare identical:
+  ///
+  /// ```swift
+  /// let d = c
+  /// print(c.isTriviallyIdentical(to: d))
+  /// // Prints true
+  /// ```
+  ///
+  /// Comparing arrays this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// array storage object. Therefore, identical arrays are guaranteed to
+  /// compare equal with `==`, but not all equal arrays are considered
+  /// identical.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    unsafe self._buffer.identity == other._buffer.identity
+  }
+}

stdlib/public/core/ArraySlice.swift

@@ -1607,3 +1607,44 @@ extension ArraySlice {
   }
 }
 #endif
+
+extension ArraySlice {
+  /// Returns a boolean value indicating whether this array is identical to
+  /// `other`.
+  ///
+  /// Two array values are identical if there is no way to distinguish between
+  /// them.
+  /// 
+  /// For any values `a`, `b`, and `c`:
+  ///
+  /// - `a.isTriviallyIdentical(to: a)` is always `true`. (Reflexivity)
+  /// - `a.isTriviallyIdentical(to: b)` implies `b.isTriviallyIdentical(to: a)`.
+  /// (Symmetry)
+  /// - If `a.isTriviallyIdentical(to: b)` and `b.isTriviallyIdentical(to: c)`
+  /// are both `true`, then `a.isTriviallyIdentical(to: c)` is also `true`.
+  /// (Transitivity)
+  /// - If `a` and `b` are `Equatable`, then `a.isTriviallyIdentical(b)` implies
+  /// `a == b`
+  ///   - `a == b` does not imply `a.isTriviallyIdentical(b)`
+  ///
+  /// Values produced by copying the same value, with no intervening mutations,
+  /// will compare identical:
+  ///
+  /// ```swift
+  /// let d = c
+  /// print(c.isTriviallyIdentical(to: d))
+  /// // Prints true
+  /// ```
+  ///
+  /// Comparing arrays this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// array storage object. Therefore, identical arrays are guaranteed to
+  /// compare equal with `==`, but not all equal arrays are considered
+  /// identical.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    self._buffer.isTriviallyIdentical(to: other._buffer)
+  }
+}

stdlib/public/core/ContiguousArray.swift

@@ -1515,3 +1515,44 @@ extension ContiguousArray {
 
 extension ContiguousArray: @unchecked Sendable
   where Element: Sendable { }
+
+extension ContiguousArray {
+  /// Returns a boolean value indicating whether this array is identical to
+  /// `other`.
+  ///
+  /// Two array values are identical if there is no way to distinguish between
+  /// them.
+  /// 
+  /// For any values `a`, `b`, and `c`:
+  ///
+  /// - `a.isTriviallyIdentical(to: a)` is always `true`. (Reflexivity)
+  /// - `a.isTriviallyIdentical(to: b)` implies `b.isTriviallyIdentical(to: a)`.
+  /// (Symmetry)
+  /// - If `a.isTriviallyIdentical(to: b)` and `b.isTriviallyIdentical(to: c)`
+  /// are both `true`, then `a.isTriviallyIdentical(to: c)` is also `true`.
+  /// (Transitivity)
+  /// - If `a` and `b` are `Equatable`, then `a.isTriviallyIdentical(b)` implies
+  /// `a == b`
+  ///   - `a == b` does not imply `a.isTriviallyIdentical(b)`
+  ///
+  /// Values produced by copying the same value, with no intervening mutations,
+  /// will compare identical:
+  ///
+  /// ```swift
+  /// let d = c
+  /// print(c.isTriviallyIdentical(to: d))
+  /// // Prints true
+  /// ```
+  ///
+  /// Comparing arrays this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// array storage object. Therefore, identical arrays are guaranteed to
+  /// compare equal with `==`, but not all equal arrays are considered
+  /// identical.
+  ///
+  /// - Complexity: O(1)
+  @_alwaysEmitIntoClient
+  public func isTriviallyIdentical(to other: Self) -> Bool {
+    unsafe self._buffer.identity == other._buffer.identity
+  }
+}

stdlib/public/core/SliceBuffer.swift

@@ -511,3 +511,29 @@ extension _SliceBuffer {
     return ContiguousArray(_buffer: result)
   }
 }
+
+extension _SliceBuffer {
+  @_alwaysEmitIntoClient
+  internal func isTriviallyIdentical(to other: Self) -> Bool {
+#if $Embedded
+    if
+      self.owner == other.owner,
+      unsafe (self.subscriptBaseAddress == other.subscriptBaseAddress),
+      self.startIndex == other.startIndex,
+      self.endIndexAndFlags == other.endIndexAndFlags
+    {
+      return true
+    }
+#else
+    if
+      self.owner === other.owner,
+      unsafe (self.subscriptBaseAddress == other.subscriptBaseAddress),
+      self.startIndex == other.startIndex,
+      self.endIndexAndFlags == other.endIndexAndFlags
+    {
+      return true
+    }
+#endif
+    return false
+  }
+}

test/stdlib/Inputs/CommonArrayTests.gyb

@@ -696,3 +696,27 @@ ${Suite}.test("${ArrayType}/AssociatedTypes") {
     indexType: Int.self,
     indicesType: CountableRange<Int>.self)
 }
+
+//===----------------------------------------------------------------------===//
+// Trivially Identical
+//===----------------------------------------------------------------------===//
+
+${Suite}.test("${ArrayType}/isTriviallyIdentical") {
+  let a1: ${ArrayType}<Int> = [ 10, 20, 30, 40 ]
+  expectTrue(a1.isTriviallyIdentical(to: a1))
+  
+  let a2: ${ArrayType}<Int> = a1
+  expectTrue(a1.isTriviallyIdentical(to: a2))
+  
+  var a3: ${ArrayType}<Int> = a2
+  a3.reserveCapacity(0)
+  expectFalse(a1.isTriviallyIdentical(to: a3))
+  
+  let a4: ${ArrayType}<Int> = [ 10, 20, 30, 40 ]
+  expectFalse(a1.isTriviallyIdentical(to: a4))
+
+  let a5: ArraySlice<Int> = a1[...]
+  let a6: ArraySlice<Int> = a1[1..<3]
+
+  expectFalse(a5.isTriviallyIdentical(to: a6))
+}