# Actor Implementations ## Topics ### Instance Methods [`func assertIsolated(@autoclosure () -> String, file: StaticString, line: UInt)`](/documentation/Swift/MainActor/assertIsolated(_:file:line:)) Stops program execution if the current task is not executing on this actor’s serial executor. [`func assumeIsolated((isolated Self) throws -> T, file: StaticString, line: UInt) rethrows -> T`](/documentation/Swift/MainActor/assumeIsolated(_:file:line:)-swift.method) Assume that the current task is executing on this actor’s serial executor, or stop program execution otherwise. [`func preconditionIsolated(@autoclosure () -> String, file: StaticString, line: UInt)`](/documentation/Swift/MainActor/preconditionIsolated(_:file:line:)) Stops program execution if the current task is not executing on this actor’s serial executor. [`func withSerialExecutor((any SerialExecutor) throws(E) -> T) throws(E) -> T`](/documentation/Swift/MainActor/withSerialExecutor(_:)-79jll) Perform an operation with the actor’s [`SerialExecutor`](/documentation/Swift/SerialExecutor). [`func withSerialExecutor(nonisolated(nonsending) (any SerialExecutor) async throws(E) -> T) async throws(E) -> T`](/documentation/Swift/MainActor/withSerialExecutor(_:)-epjy) Perform an operation with the actor’s [`SerialExecutor`](/documentation/Swift/SerialExecutor). --- 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)