How Stella Got Her @NoEscape Back

NSManagedObjectContext.swift

// Swift 3 only; `@noescape` only applies to function definitions (not function types) in 2.x.

import CoreData

extension NSManagedObjectContext {
    func performAndWaitOrThrow<Return>(_ body: () throws -> Return) rethrows -> Return {
        func impl(execute work: () throws -> Return, recover: (Error) throws -> Void) rethrows -> Return {
            var result: Return!
            var error: Error?

            // performAndWait is marked @escaping as of iOS 10.0.
            typealias Fn = (() -> Void) -> Void
            let performAndWaitNoescape = unsafeBitCast(self.performAndWait, to: Fn.self)
            performAndWaitNoescape {
                do {
                    result = try work()
                } catch let e {
                    error = e
                }
            }

            if let error = error {
                try recover(error)
            }
            
            return result
        }

        return try impl(execute: body, recover: { throw $0 })
    }
}


let context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

struct SomeError: Error {}

do {
    let value: Int = try context.performAndWaitOrThrow {
        throw SomeError()
    }

    print(value)
} catch {
    print(error)
}

Any idea whether this was an oversight during the great renamification? Or is it intentionally @escaping? They’ve been so nicely diligent providing DispatchQueue’s func sync<T>(execute: () throws -> T) rethrows -> T. Have you reported this as a bug?