SwiftExceptionBridge

Disclaimer

• I am very happy Swift does not have exceptions, I much rather hope to see a later addition of Computational Expressions or so.
• I do not want to encourage you to use exceptions.
• By default exceptions leak memory when combined with ARC (you can use clang -fobjc-arc-exceptions).
• Unfortunately, there are times when you can't get around catching an exception (NSTask, NSFileHandle, KVO, ...) in Cocoa and currently Swift doesn't allow you to do so.
• This is a quick prototype not ready for production probably.
• This repo contains a full Xcode project including all the code (Swift and ObjC).

Proposed Workaround

The following interface

@interface JFWSwiftExceptionBridge : NSObject

+ (void)swiftBridgeTry:(void(^)(void))tryBlock
                except:(void(^)(NSException *))exceptBlock
               finally:(void(^)(void))finallyBlock;

+ (void)swiftBridgeTry:(void(^)(void))tryBlock
                except:(void(^)(NSException *))exceptBlock;

+ (JFWResultOrException *)swiftBridgeResultTry:(id(^)(void))tryBlock;

@end

does allow you to use them from Swift (full swift example). Example:

A full try/catch/finally:

JFWSwiftExceptionBridge.swiftBridgeTry({
    exceptionThrowingFunction()
    },
    except: {
        print("CAUGHT EXCEPTION: \($0)\n")
        },
    finally: {
        () -> Void in
        print("FINALLY\n")
})

Try/catch only:

JFWSwiftExceptionBridge.swiftBridgeTry(exceptionThrowingFunction,
    except: {
        print("CAUGHT EXCEPTION: \($0)\n")
})

Or rather an Either-like type which wraps either the result (type id) as returned from the function or the exception if the function threw an exception:

let roe = JFWSwiftExceptionBridge.swiftBridgeResultTry { () -> AnyObject! in
    return exceptionTrowingFunctionWithResult()
}
print("RESULT OR EXCEPTION: \(roe)\n")

The output then looks either like

RESULT OR EXCEPTION: Result(works)

if it worked and the string "works" was returned, or like that

RESULT OR EXCEPTION: Exception(<DESCRIPTION OF EXCEPTION>)

if an exception appeared.