[Pitch #2] Add `isKnownIdentical` Method for Quick Comparisons to `Equatable`

vanvoorden · June 20, 2025, 7:23am

There's also this public-but-underscored example on Sequence:

Here is the default implementation that returns nil:

stdlib/public/core/Sequence.swift

swift-6.1.2-RELEASE


      
          public func _customContainsEquatableElement(
            _ element: Iterator.Element
          ) -> Bool? {
            return nil
          }

And here's where we use that nil to perform some conditional logic:

github.com/swiftlang/swift

stdlib/public/core/SequenceAlgorithms.swift

swift-6.1.2-RELEASE


      
            public func contains(_ element: Element) -> Bool {
              if let result = _customContainsEquatableElement(element) {
                return result
              } else {
                return self.contains { $0 == element }
              }
            }
          }