The 2nd Monitor

Welp, now I'm annoyed with Swift again.

In Objective-C, you could throw exceptions and you could use try-catch blocks, but both were heavily, heavily discouraged.

In Swift, you plain can't use try-catch blocks.

How are errors handled then? On Error GoTo? ;)

@sim napalm'd - and good night!

In Swift?

just kidding. but yeah, in Swift

enum ServerResponse {
    case Result(String, String)
    case Error(String)
}

let success = ServerResponse.Result("6:00 am", "8:09 pm")
let failure = ServerResponse.Error("Out of cheese.")

switch success {
case let .Result(sunrise, sunset):
    let serverResponse = "Sunrise is at \(sunrise) and sunset is at \(sunset)."
case let .Error(error):
    let serverResponse = "Failure...  \(error)"
}

12:36 AM

ok, so return values.

Dan Pantry

that looks like f#

> From Apple news books, "Using Swift with Cocoa and Objective-C". Runtime exceptions not occur using swift languages, so that's why you don't have try-catch.

what happens when there's, say, a division by zero?

Q: Error-Handling in Swift-Language

39

I haven't read too much into Swift but one thing that i noticed is there are no exceptions. So how do they do error handling in swift? Has anyone found anything to error-handling?

swift

Division by 0 isn't an exception in Swift or Objective-C. It's undefined behavior (tends to return 0).

> However, as documentation suggests it is running on the same runtime as ObjC, and therefore you are still able to throw NSExceptions

12:38 AM

Yeah, I don't know.

I'm sure you could throw an NSException. You certainly can't catch one.

Q: Increase the speed of this Caesar Cipher?

0

Here's my attempt at a Caesar Cipher encoder/decoder. If given a key, it will encrypt the given string. However, if you do not specify a key, it checks each of the 26 possible keys and returns the one with the highest percentage of words that appear in this file of English words (with a couple a...

performance python-2.7 caesar-cipher

Welp, Swift playgrounds are certainly not the place to do Project Euler stuff.

Q: what approach should be used i am so lost

12:57 AM

0

public static int getMenuOption() public static double getOperand(String prompt) public static double add(double operand1, double operand2) public static double subtract(double operand1, double operand2) public static double multiply(double operand1, double operand2) public static double divide(d...

java mathematics basic

Man, someone at Apple really hates exceptions.

An OO language without exceptions is just strange.

It's just a different design philosophy. Although, I much prefer the Objective-C approach rather than the Swift approach.

It's just odd that their driving motivation was to get rid of the C in Objective C, but they're still apparently sticking with C style error checking (though with slightly prettier syntax).

So, in Objective-C, things that are rare but not completely unexpected in a properly coded program are errors.

Generally speaking, things that could be prevented by the programmer (like out of bounds exceptions) are exceptions.

programming-challenge palindrome swift

0

Q: Project Euler #4 in Swift

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99. Find the largest palindrome made from the product of two 3-digit numbers. What I've so far learned about Swift is that while the Playground is very cool ...

1:11 AM

So try-catches are shunned because you shouldn't be writing code that throws exceptions.

But consider this block of Swift code:

extension Int {
    func reversed() -> Int {
        var original: Int = self
        var reversed: Int = 0

        while original > 0 {
            reversed *= 10
            reversed += original % 10
            original /= 10
        }

        return reversed
    }
}

let bigInt: Int = Int.max - 8

let overflow = bigInt.reversed()

Makes sense (if you're into C error handling), but it's still strange to not have exceptions at all. There's still asserts and return codes, of course, but... meh.

I don't know. I think it's just as an ObjC/swift outsider, it's a little weird.

Though I did ObjC for 6 months, and the error handling never quite felt pleasant.

But then again, exceptions can be just as unpleasant

So, Int.max - 8 is: 9,223,372,036,854,775,799

If you reverse that, it's > Int.max, so it overflows

I think in Objective-C, it'd just be undefined behavior (integer overflow)

Guess what happens in Swift?

Playground execution failed: error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).
The process has been left at the point where it was interrupted, use "thread return -x" to return to the state before expression evaluation.
* thread #1: tid = 0x13299, 0x000000010f61d82c, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x000000010f61d82c

EXC_BAD_INSTRUCTION sounds like an exception to me... no?

That's.... hrmmm.... If static analysis can pick up the possibility of that, it's great, but otherwise, damn, you just crashed a program.

@Mat'sMug I think it's an interrupt from the processor

"EXC"

1:17 AM

Hrmm, yeah after a google, it definitely seems to be a runtime-level exception.

By the way, that's the description I get in the playground.

Which is more helpful than what I get if I actually compile the code and run it in a real project

Thread 1: EXC_BAC_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

Actually nevermind, I think I have all the information I got in the playground, it's just presented differently.

Every error doesn't necessarily need to be an exception, but they're a very nice facility to have. I think it just comes down to Apple clearly has a different philosophy than I do.

Yeah. Like I said, it's a different philosophy.

I started exception handling in Java actually, and never really liked it.

I just never feel quite safe with C style error handling. what if i forgot to check an error code? suddenly I have a program with some rather odd, sporadic behavior, and I'm going to have a hell of a time tracking that down. Uncaught exceptions leave a much better debugging trail, and they give me a peace of mind that my code is reasonably robust.

Then again, I guess typical code really doesn't have that much error handling. It's just low level or library type things.

Right, that's the thing...

Your low level stuff, write your exceptions and try catches if need be

1:24 AM

And unit testing could theoretically give relatively high confidence of error handling...

But higher level stuff, you shouldn't have try-catches in a view controller.

Well, you shouldn't have ObjC style exceptions in a VC

In other languages, people would say you shouldn't typically be checking error codes in high level code

But, meh. I suppose it really is just different worlds. And we've each chosen a side, haha

Objective-C style error handling though gives me the option to check for the error.

If it doesn't matter whether or not the method errors out, I don't have to bother writing error handling code.

I'd much rather the program terminate in the case of an unhandled error than continue chugging along on invalid data/resources.

But it's not necessarily invalid data

1:28 AM

Well, if that's the case, I'll just ignore the exception. But that's typically not the case.

There are very few times when I truly, really do not care if something fails.

99.9% of the time, if I'm not checking for an error, I'm just being lazy.

"just ignore the exception", but you still have to write your try-catch block or crash.

Correct. I prefer to have to say "hey, ignore this error," than to have to say, "I do care about this error."

I'd rather opt out than opt in with regards to error handling.

I think this is the Apple philosophy...

If the app crashes, dumb users might potentially wrongly blame the operating system or the hardware.

If the app has bad/wrong data, dumb users will correctly blame the app.

That matches their approach to how they handle iOS apps doing background tasks.

Hrmmm, I think users tend to blame apps crashing on the app.

But maybe I overestimate the average person's understanding of programs :/

I do, for sure, but the average user is a raly dum moran.

And when you're Apple, both the device AND the OS are your product.

There are millions of apps on the app store, and Apple gets a piece of all of their profits. But what's ultimately most important to them is that the user not be led to believe that the operating system or the device are bad.

1:34 AM

Eh, I think we're overestimating users' stupidity and Apple's paranoia. I surely hope this wasn't the driving motivation of their decision.

Difference in philosophy I'll accept, but this is almost malicious :/

Well, malicious is far too strong of word

But rather priorities in the wrong place

I don't know that that's the driving motivation for the error handling, but it's absolutely the driving motivation for a lot of other things.

The best example being what I already mentioned--how iOS handles allowing apps to do things in the background. Are you familiar with it?

not particularly

mjolka

@nhgrif in that question, do you need these lines? var left: Int = 999 var right: Int = 999

Nope. Good catch.

Anyway, Corbin, unless your app is in one of a very few specific categories, to do stuff in the background, you register with the OS as an app that wants to do background stuff.

As well, you set a minimum time between updates. You can't set a maximum, but you can set a minimum (so you only do a background task once per hour at most, for example)

Whenever the OS deems it convenient, it wakes your app up with a method to the app delegate. It passes in a function pointer.

You have 30 seconds to execute code, and then call the function that was passed in with one of three arguments, which indicates "No new data," "new data," or "error".

Using your apps returns from this function, as well as a ton of other metrics such as current device battery life, how busy the processor currently is, how frequently the user uses your app, etc., the device decides when you get to do background updates.

1:55 AM

Are you teaching yourself Swift via reviewing my Project Eulers? ;) — nhgrif 16 secs ago

@rolfl "The print in the function is.... ugly." For the record... it originally wasn't, but I wanted to move it into the printTimeElapsedWhenRunningCode

But for the future Project Euler solutions, I'm going to take this approach:

func solution() {
    let firstTwentyInts: [Int] = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
    let answer: Int = leastCommonMultiple(firstTwentyInts)

    println(String(answer))
}

printTimeElapsedWhenRunningCode("Least Common Multiple", solution)

RubberDuck

Yes @Simon. I was challenged to do the ice bucket thing. It annoys me too, but I've never been one to turn down a dare.

@nhgrif apple.com/ca/pr/library/2014/07/…

I figure I should at least be able to recognize the code.

Hmm?

Do you work for IBM?

yup

Ah, I see.

I did not know that.

I've already got PE#5 worked out. I'm trying to space out my questions at least 12ish hours though.

2:11 AM

@nhgrif - I believe a novice reviewing an expert's code is often a good thing.... it makes the expert stop and think about how people see them think, and how they express things.

I know nothing about swift, but I can see algorithm and other issues in your code.

Well, I don't consider myself an expert, but you are right.

I can read the manual pages enough to know what should be possible.

I'm focusing on other things and forgetting about some of the things you point out, which would be obvious to me if I were writing Objective-C actually

Put it together, I will get enough of an ability to read swift to know when people are doing the right thng, and when people are trying to BS me ;-)

Youa re doing the right thing, but I can see those 'lazy' decisions too. I use the word lazy like a true programmer would. Normally lazy is good. but on code review, we strive for better uses of lazy

Also, about your questions, Apart from the two swift ones I did (one last night, and one today), I have not answered any main-site questions for almost a week.

Meta has taken up most of my allotment of CR time.

@nhgrif eh that's just basic resource sharing though. All OS's do that, just not to such a great extent, since windowing gives you a more visible control over background processes typically. It is interesting though that there's no guaranteed minimal period to be called again. It makes sense though.

2:16 AM

My recent ratio is 5 to 1, 5 meta answers for each swift answer int he past 7 days.

Jamal

I'm kinda falling behind on Meta answers, though I feel others already have good answers.

@rolfl I think that makes it pretty much all my questions though. ;)

@Corbin It's my understand though that the OS builds a usage pattern from each individual user's usage of your app.

2:33 AM

0

Q: Pokemon Type Evaluator

Thought I would apply what I learned to make something fun. Its purpose is to type check pokemon for anyone familiar with the series. It mostly works but I have two concerns. First, Sometimes you write code and you get the pervading feeling you're not using some method, some API or the best appr...

java beginner swing

If you only use my app once a day and you always use it around 7am, then no matter what I set my background stuff up for, it's very likely that the OS will eventually optimize it so that my app only gets opportunity to check for updates once between 6am and 6:59am and then at no other part of the day.

I've only just started using this stuff though, so I'm not certain exactly how good it is, but supposedly it's extraordinarily good at doing no more than absolutely necessary.

2:46 AM

that's pretty cool then. makes me feel a lot better about having like 500 apps open at any time haha

As long as you've got an iOS device.

Android, of course is less limiting, which has its advantages. And if the user knows what they're doing, they can potentially get more out of their Android device than they can their iOS device.

But if the user doesn't really know what they're doing, and they download some nefarious app that's doing stuff in the background, well now their app is massively draining the device's battery, or using up RAM, or competing for processor time.

And to you or I or anyone who knows what they're doing, we start looking at what's going on with the device, and try to find out why we're getting poor performance.

But to the average, less tech-savvy user, there's a huge optics problem.

Because the actual problem is in the background... where a less tech savvy user won't notice it.

They are more likely to associate the poor performance with the active app or the poor battery life with the device.

3:04 AM

android seems to trust applications more while simultaneously having very few checks in place to actually make sure that trust is warranted

it's kind of scary sometimes :/

3:15 AM

hmm

Q: Clean design for the MVC pattern with view latency

3:35 AM

0

It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane...

design-patterns

5:56 AM

Monking

mjolka

@skiwi monking :)

Still asleep... will change in a bit when I go to work in 10 degrees outside :| in August

Phrancis

6:12 AM

10 C I hope?

Q: Find the index of the element

-2

can somebody give me a java program which will find the index of the element whose value is the sum of the remaining elements. I have to tried to write the code but I couldnt write a simplified code. Iam myself writing a cumbersome logic but couldnt simplify it. can anybody help me in resolving...

java

6:37 AM

Yes, cycling in 6 degrees definitely woke me up.