[RFC][DNM] Add isIdentical Methods for Quick Comparisons to String and Substring

benchmark/single-source/StringTests.swift

@@ -49,6 +49,13 @@ public var benchmarks: [BenchmarkInfo] {
         runFunction: run_iterateWords,
         tags: [.validation, .String]))
   }
+  if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *) {
+    result.append(
+      BenchmarkInfo(
+        name: "StringIdentical",
+        runFunction: run_StringIdentical,
+        tags: [.validation, .String]))
+  }
   return result
 }
 
@@ -1676,3 +1683,14 @@ public func run_iterateWords(_ n: Int) {
     blackHole(swiftOrgHTML._words)
   }
 }
+
+@available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *)
+public func run_StringIdentical(_ n: Int) {
+  let str1 = "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. "
+  let str2 = str1
+  for _ in 0 ..< n {
+    for _ in 0 ..< 100_000 {
+      check(str1.isIdentical(to: str2))
+    }
+  }
+}

benchmark/single-source/SubstringTest.swift

@@ -12,25 +12,36 @@
 
 import TestsUtils
 
-public let benchmarks = [
-  BenchmarkInfo(name: "EqualStringSubstring", runFunction: run_EqualStringSubstring, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "EqualSubstringString", runFunction: run_EqualSubstringString, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "EqualSubstringSubstring", runFunction: run_EqualSubstringSubstring, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "EqualSubstringSubstringGenericEquatable", runFunction: run_EqualSubstringSubstringGenericEquatable, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringRemoveFirst1", runFunction: run_SubstringRemoveFirst1, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringRemoveLast1", runFunction: run_SubstringRemoveLast1, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "LessSubstringSubstring", runFunction: run_LessSubstringSubstring, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "LessSubstringSubstringGenericComparable", runFunction: run_LessSubstringSubstringGenericComparable, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "StringFromLongWholeSubstring", runFunction: run_StringFromLongWholeSubstring, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "StringFromLongWholeSubstringGeneric", runFunction: run_StringFromLongWholeSubstringGeneric, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringComparable", runFunction: run_SubstringComparable, tags: [.validation, .api, .String],
-    setUpFunction: { blackHole(_comparison) }),
-  BenchmarkInfo(name: "SubstringEqualString", runFunction: run_SubstringEqualString, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringEquatable", runFunction: run_SubstringEquatable, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringFromLongString2", runFunction: run_SubstringFromLongString, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringFromLongStringGeneric2", runFunction: run_SubstringFromLongStringGeneric, tags: [.validation, .api, .String]),
-  BenchmarkInfo(name: "SubstringTrimmingASCIIWhitespace", runFunction: run_SubstringTrimmingASCIIWhitespace, tags: [.validation, .api, .String]),
-]
+public var benchmarks: [BenchmarkInfo] {
+  var result = [
+    BenchmarkInfo(name: "EqualStringSubstring", runFunction: run_EqualStringSubstring, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "EqualSubstringString", runFunction: run_EqualSubstringString, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "EqualSubstringSubstring", runFunction: run_EqualSubstringSubstring, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "EqualSubstringSubstringGenericEquatable", runFunction: run_EqualSubstringSubstringGenericEquatable, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringRemoveFirst1", runFunction: run_SubstringRemoveFirst1, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringRemoveLast1", runFunction: run_SubstringRemoveLast1, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "LessSubstringSubstring", runFunction: run_LessSubstringSubstring, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "LessSubstringSubstringGenericComparable", runFunction: run_LessSubstringSubstringGenericComparable, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "StringFromLongWholeSubstring", runFunction: run_StringFromLongWholeSubstring, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "StringFromLongWholeSubstringGeneric", runFunction: run_StringFromLongWholeSubstringGeneric, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringComparable", runFunction: run_SubstringComparable, tags: [.validation, .api, .String],
+      setUpFunction: { blackHole(_comparison) }),
+    BenchmarkInfo(name: "SubstringEqualString", runFunction: run_SubstringEqualString, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringEquatable", runFunction: run_SubstringEquatable, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringFromLongString2", runFunction: run_SubstringFromLongString, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringFromLongStringGeneric2", runFunction: run_SubstringFromLongStringGeneric, tags: [.validation, .api, .String]),
+    BenchmarkInfo(name: "SubstringTrimmingASCIIWhitespace", runFunction: run_SubstringTrimmingASCIIWhitespace, tags: [.validation, .api, .String]),
+  ]
+
+  if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *) {
+    result.append(
+      BenchmarkInfo(
+        name: "SubstringIdentical",
+        runFunction: run_SubstringIdentical,
+        tags: [.validation, .String]))
+  }
+  return result
+}
 
 // A string that doesn't fit in small string storage and doesn't fit in Latin-1
 let longWide = "fὢasὢodὢijὢadὢolὢsjὢalὢsdὢjlὢasὢdfὢijὢliὢsdὢjøὢslὢdiὢalὢiὢ"
@@ -332,3 +343,12 @@ public func run _LessSubstringSubstringGenericStringProtocol(_ n: Int) {
   }
 }
 */
+
+@inline(never)
+@available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *)
+public func run_SubstringIdentical(_ n: Int) {
+  let (a, b) = (ss1, ss1)
+  for _ in 1...n*500 {
+    blackHole(a.isIdentical(to: b))
+  }
+}

stdlib/public/core/String.swift

@@ -1112,4 +1112,23 @@ extension String {
   }
 }
 
-
+@available(SwiftStdlib 6.3, *)
+extension String {
+  /// Returns a boolean value indicating whether this string is identical to
+  /// `other`.
+  ///
+  /// Two string values are identical if there is no way to distinguish between
+  /// them.
+  ///
+  /// Comparing strings this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// string storage object. Therefore, identical strings are guaranteed to
+  /// compare equal with `==`, but not all equal strings are considered
+  /// identical.
+  ///
+  /// - Performance: O(1)
+  @available(SwiftStdlib 6.3, *)
+  public func isIdentical(to other: Self) -> Bool {
+    self._isIdentical(to: other)
+  }
+}

stdlib/public/core/Substring.swift

@@ -1307,3 +1307,45 @@ extension Substring {
     return Substring(_unchecked: Slice(base: base, bounds: r))
   }
 }
+
+extension Substring {
+  /// Returns a boolean value indicating whether this substring is identical to
+  /// `other`.
+  ///
+  /// Two substring values are identical if there is no way to distinguish
+  /// between them.
+  ///
+  /// Comparing substrings this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// substring storage object. Therefore, identical substrings are guaranteed
+  /// to compare equal with `==`, but not all equal substrings are considered
+  /// identical.
+  ///
+  /// - Performance: O(1)
+  @_alwaysEmitIntoClient
+  public func _isIdentical(to other: Self) -> Bool {
+    self._wholeGuts.rawBits == other._wholeGuts.rawBits &&
+    self._offsetRange == other._offsetRange
+  }
+}
+
+@available(SwiftStdlib 6.3, *)
+extension Substring {
+  /// Returns a boolean value indicating whether this substring is identical to
+  /// `other`.
+  ///
+  /// Two substring values are identical if there is no way to distinguish
+  /// between them.
+  ///
+  /// Comparing substrings this way includes comparing (normally) hidden
+  /// implementation details such as the memory location of any underlying
+  /// substring storage object. Therefore, identical substrings are guaranteed
+  /// to compare equal with `==`, but not all equal substrings are considered
+  /// identical.
+  ///
+  /// - Performance: O(1)
+  @available(SwiftStdlib 6.3, *)
+  public func isIdentical(to other: Self) -> Bool {
+    self._isIdentical(to: other)
+  }
+}

test/stdlib/StringAPI.swift

@@ -533,4 +533,62 @@ StringTests.test("hasPrefix/hasSuffix vs Character boundaries") {
   expectFalse(s2.hasSuffix("\n"))
 }
 
+StringTests.test("isIdentical(to:) small ascii")
+.skip(.custom(
+  { if #available(SwiftStdlib 6.3, *) { false } else { true } },
+  reason: "Requires Swift 6.3's standard library"
+))
+.code {
+  guard #available(SwiftStdlib 6.3, *) else { return }
+
+  let a = "Hello"
+  let b = "Hello"
+
+  precondition(a == b)
+
+  expectTrue(a.isIdentical(to: a))
+  expectTrue(b.isIdentical(to: b))
+  expectTrue(a.isIdentical(to: b)) // Both small ASCII strings
+  expectTrue(b.isIdentical(to: a))
+}
+
+StringTests.test("isIdentical(to:) small unicode")
+.skip(.custom(
+  { if #available(SwiftStdlib 6.3, *) { false } else { true } },
+  reason: "Requires Swift 6.3's standard library"
+))
+.code {
+  guard #available(SwiftStdlib 6.3, *) else { return }
+
+  let a = "Cafe\u{301}"
+  let b = "Cafe\u{301}"
+  let c = "Café"
+
+  precondition(a == b)
+  precondition(b == c)
+
+  expectTrue(a.isIdentical(to: b))
+  expectTrue(b.isIdentical(to: a))
+  expectFalse(a.isIdentical(to: c))
+  expectFalse(b.isIdentical(to: c))
+}
+
+StringTests.test("isIdentical(to:) large ascii")
+.skip(.custom(
+  { if #available(SwiftStdlib 6.3, *) { false } else { true } },
+  reason: "Requires Swift 6.3's standard library"
+))
+.code {
+  guard #available(SwiftStdlib 6.3, *) else { return }
+
+  let a = String(repeating: "foo", count: 1000)
+  let b = String(repeating: "foo", count: 1000)
+
+  precondition(a == b)
+
+  expectFalse(a.isIdentical(to: b)) // Two large, distinct native strings
+  expectTrue(a.isIdentical(to: a))
+  expectTrue(b.isIdentical(to: b))
+}
+
 runAllTests()