Open Radar

 
This code compiles:

extension Array {
    func withUnsafeBufferPointer<R>(@noescape body: (UnsafeBufferPointer<T>) throws -> R) throws -> R {
        return try self.withUnsafeBufferPointer { buf in
            return Result{try body(buf)}}.value()
    }
}

This code, which should be identical, returns an error “Closure use of @noescape parameter 'body' may allow it to escape” (also “could not find member ‘value’, but I believe that comes from the first):

extension Array {
    func withUnsafeBufferPointer<R>(@noescape body: (UnsafeBufferPointer<T>) throws -> R) throws -> R {
        return try self.withUnsafeBufferPointer {
            return Result{try body($0)}}.value()
    }
}

The code should be treated the same whether we name the closure parameter or use $0.

Additional code that this calls:

enum Result<T> {
    case Success(T)
    case Failure(ErrorType)

    func value() throws -> T {
        switch self {
        case .Success(let value): return value
        case .Failure(let err): throw err
        }
    }

    init(@noescape f: () throws -> T) {
        do {
            self = .Success(try f())
        } catch {
            self = .Failure(error)
        }
    }
}