UnsafeContinuation
A mechanism to interface between synchronous and asynchronous code, without correctness checking.
Declaration
@frozen struct UnsafeContinuation<T, E> where E : ErrorOverview
A continuation is an opaque representation of program state. To create a continuation in asynchronous code, call the withUnsafeContinuation(_:) or withUnsafeThrowingContinuation(_:) function. To resume the asynchronous task, call the resume(returning:), resume(throwing:), resume(with:), or resume() method.
CheckedContinuation performs runtime checks for missing or multiple resume operations. UnsafeContinuation avoids enforcing these invariants at runtime because it aims to be a low-overhead mechanism for interfacing Swift tasks with event loops, delegate methods, callbacks, and other non-async scheduling mechanisms. However, during development, the ability to verify that the invariants are being upheld in testing is important. Because both types have the same interface, you can replace one with the other in most circumstances, without making other changes.