# ~=(_:_:) Returns a Boolean value indicating whether an argument matches `nil`. ``` static func ~= (lhs: _OptionalNilComparisonType, rhs: borrowing Wrapped?) -> Bool ``` ## Parameters `lhs` A `nil` literal. `rhs` A value to match against `nil`. ## Discussion You can use the pattern-matching operator (`~=`) to test whether an optional instance is `nil` even when the wrapped value’s type does not conform to the `Equatable` protocol. The pattern-matching operator is used internally in `case` statements for pattern matching. The following example declares the `stream` variable as an optional instance of a hypothetical `DataStream` type, and then uses a `switch` statement to determine whether the stream is `nil` or has a configured value. When evaluating the `nil` case of the `switch` statement, this operator is called behind the scenes. ``` var stream: DataStream? = nil switch stream { case nil: print("No data stream is configured.") case let x?: print("The data stream has \(x.availableBytes) bytes available.") } // Prints "No data stream is configured." ``` > Note: To test whether an instance is `nil` in an `if` statement, use the > equal-to operator (`==`) instead of the pattern-matching operator. The > pattern-matching operator is primarily intended to enable `case` > statement pattern matching. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)