[RFC][DNM] Add isIdentical Methods for Quick Comparisons to AttributedString and AttributedSubstring

Benchmarks/Benchmarks/AttributedString/BenchmarkAttributedString.swift

@@ -431,6 +431,10 @@ let benchmarks = {
         blackHole(manyAttributesString == manyAttributesString2)
     }
 
+    Benchmark("isIdentical") { benchmark in
+        blackHole(manyAttributesString.isIdentical(to: manyAttributesString))
+    }
+
     Benchmark("equalityDifferingCharacters") { benchmark in
         blackHole(manyAttributesString == manyAttributesString3)
     }
@@ -442,7 +446,11 @@ let benchmarks = {
     Benchmark("substringEquality") { benchmark in
         blackHole(manyAttributesSubstring == manyAttributes2Substring)
     }
-
+
+    Benchmark("substringIsIdentical") { benchmark in
+        blackHole(manyAttributesSubstring.isIdentical(to: manyAttributesSubstring))
+    }
+
     Benchmark("hashAttributedString") { benchmark in
         var hasher = Hasher()
         manyAttributesString.hash(into: &hasher)

Sources/FoundationEssentials/AttributedString/AttributedString.swift

@@ -403,3 +403,22 @@ extension Range where Bound == BigString.Index {
         Range<AttributedString.Index>(uncheckedBounds: (AttributedString.Index(lowerBound, version: version), AttributedString.Index(upperBound, version: version)))
     }
 }
+
+extension AttributedString {
+  /// 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)
+  public func isIdentical(to other: Self) -> Bool {
+    self._guts === other._guts
+  }
+}

Sources/FoundationEssentials/AttributedString/AttributedSubstring.swift

@@ -205,3 +205,23 @@ extension AttributedSubstring {
         }
     }
 }
+
+extension AttributedSubstring {
+  /// 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)
+  public func isIdentical(to other: Self) -> Bool {
+    self._guts === other._guts &&
+    self._range == other._range
+  }
+}

Tests/FoundationEssentialsTests/AttributedString/AttributedStringTests.swift

@@ -33,6 +33,14 @@ import AppKit
 #endif
 #endif
 
+func createManyAttributesString() -> AttributedString {
+    var str = AttributedString("a")
+    for i in 0..<10000 {
+        str += AttributedString("a", attributes: AttributeContainer().testInt(i))
+    }
+    return str
+}
+
 /// Regression and coverage tests for `AttributedString` and its associated objects
 @Suite("AttributedString")
 private struct  AttributedStringTests {
@@ -360,6 +368,15 @@ private struct  AttributedStringTests {
         #expect(a2.characters.elementsEqual(a3.characters))
     }
 
+    @Test func attributedStringIdentical() {
+        let manyAttributesString = createManyAttributesString()
+        let manyAttributesString2 = createManyAttributesString()
+        #expect(manyAttributesString.isIdentical(to: manyAttributesString))
+        #expect(manyAttributesString2.isIdentical(to: manyAttributesString2))
+        #expect(!(manyAttributesString.isIdentical(to: manyAttributesString2)))
+        #expect(!(manyAttributesString2.isIdentical(to: manyAttributesString)))
+    }
+
     @Test func attributedSubstringEquality() {
         let emptyStr = AttributedString("01234567890123456789")
 
@@ -389,7 +406,19 @@ private struct  AttributedStringTests {
 
         #expect(emptyStr[index0 ..< index5] == AttributedString("01234"))
     }
-
+
+    @Test func attributedSubstringIdentical() {
+        let manyAttributesString = createManyAttributesString()
+        let manyAttributesString2 = createManyAttributesString()
+        let manyAttributesStringRange = manyAttributesString.characters.index(manyAttributesString.startIndex, offsetBy: manyAttributesString.characters.count / 2)...
+        let manyAttributesSubstring = manyAttributesString[manyAttributesStringRange]
+        let manyAttributes2Substring = manyAttributesString2[manyAttributesStringRange]
+        #expect(manyAttributesSubstring.isIdentical(to: manyAttributesSubstring))
+        #expect(manyAttributes2Substring.isIdentical(to: manyAttributes2Substring))
+        #expect(!(manyAttributesSubstring.isIdentical(to: manyAttributes2Substring)))
+        #expect(!(manyAttributes2Substring.isIdentical(to: manyAttributesSubstring)))
+    }
+
     @Test func runEquality() {
         var attrStr = AttributedString("Hello", attributes: AttributeContainer().testInt(1))
         attrStr += AttributedString(" ")