Rust Programming Language Programmieren in Rust (Full lecture, German), 18 Nov 2016

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From YouTube: Programmieren in Rust (14.11.): Error Handling

Description

Vorlesung „Programmieren in Rust“ an der Universität Osnabrück im Wintersemester 2016/17.

Dies ist die Aufnahme des Beamerbildes sowie des Notebook-Mikrofons. Alternative Aufnahme (mit Dozentenvideo): https://video4.virtuos.uos.de/engage/theodul/ui/core.html?id=2efa047b-8c2a-4545-bd6b-3c36d208f33f

Slides und weitere Informationen: https://github.com/LukasKalbertodt/programmieren-in-rust

Playlist: https://www.youtube.com/playlist?list=PL0Ur-09iGhpwMbNiVTBeHmIjs0GuIXhNg

A

Or rather, seventh lectures rast, it's already on. I think we'll proceed a bit slower as announced or this whole week, we'll proceed a bit slower this week is actually about error handling and how we deal with errors. Rast friends, a few things, the I once say: people once again hand in the change on Sunday evening. That was now the last week where we are still gracious and maybe turned a blind eye from next week.

A

It will be really very strict, so which comes with every computer had a time stamp, which cow with not for sunday at 12 o'clock is just not observed. Just have to be so strict, so he is between the teams and start received very early. The others would still be observed, so we just have to be strict.

A

Then another thing I saw that many of you are still struggling with travis because of as simple as spaces set up simple editor. Any sane editor can be set up to do this automatically. Now this is monkey work. You don't want to do it yourself, always remove the spaces and add the new line also says in the editor. It should be easier, then you'll never have problems with it again then another important one, of course that's important, as always I said recently gone to the crew. That means but gone gone, write it briefly.

A

Again it was a data structure.

A

That will be gone very apparently I didn't know, and the last thing is that we can now upgrade the compiler, so you have been able to since about friday, but I'll just say that now we will also start with it, because the puppet task is to go through a bit, in particular to go through the sample solution.

A

This time it is light on black. You can see that there are 14 still wonderful. We will have a look first, you can so everyone who has already installed it by branch can say update and then it automatically does a few things for me. I 'm, already on the current version of you, unfortunately, version. 1.3 is ten down, that happens every six weeks, by the way,.

A

That's why I'll, let you know every now and then that I'll get the latest changes,, not that it's absolutely necessary,, but it gets better with every version,, ok and if we want to update rast ab ourselves. This is now also a program just says rust from 11 update. And yes, that's up to me too.

A

We want to take a look at the pokémon program. Now that was the bigger task that the others would also look at what would happen? You say the first task.

B

A

Couple say: yes, panic just started saying: yes,.

A

Ok, how than how difficult would that then estimate he found it even if that were super super trivial and just rare. That was pretty difficult, because more than two three hours were spent. Ok,.

A

Then simply to the others are with ok, interesting that there are so big differences, so.

A

Yeah that can be try. One thing I don't always want to look there I'll try to mirror the screen now without my recording getting broken, then it's. It just hope for a bit that it works.

A

The recording do you do something, then let 's just hope that it works. Ok, so let's go through it very slowly. The first task was, I think this advised input to complete. It is right that I already have a great coach part that gives you a string from the command line 1, and this team will already check that there are still 0 1 1 in it as a character, but you have to convert the signal.

A

Don't worry about this code for now it's about this one code then go at the beginning of vector that want to return is a lector, so return a list and say here. If I tell the users, we can say directly how long that is. We can. We know how long the rector is, but why do we know how long it vector isn't that usually in string, especially unicode characters in it and input of the last string user take the longer ones? That's the payment and not the unicode characters.

A

In the string, villages are now the characters are stored 1 year, but we are.

B

A

But exactly right, but this recognizes being longer because we have the unicode in it, yes, long unicode characters,, because we can be larger than one,.

A

Right, here,, 0 1, still in the ascii area, and we said that they are compatible,. So that's exactly why only one correct one is correct that about such an optimization. They are not absolutely necessary.

A

If you want to write code first, just write it down quickly, then it is not absolutely necessary that you think something like that, but you can keep that in the back of your mind, so that you play too slowly for that you get if you can call up such extra constructors, yes,, and this is an old loop that you already know from previous tasks,. We just say strings, and then we can repair them through the whole character and now that's a great trick because of this expression here.

A

That already gives him a boule back here. I would otherwise write something like that. The fc straight away, 1 then does something and then does something else that here where the conditions are. It says that these conditions must of course be goulian, so he has to come back to the boullion and since this expression can already be evaluated for bulin,, this google can push the rain directly away.

A

It's pretty short, that makes sense,. It's still unclear. Why it works,.

A

Well,, let's continue,, then the path is simply returned,, so that was n't absolutely necessary. No, but what she does you notice as me, always that you expect that too, or so, I'm actually quite enthusiastic about the system. We have right now, because that way, we can really always tell you what we can do. Better,, for example, that many of you are right a lot of writing. So it was kind of normal that you wrote it like that, of.

A

Course, it’s also okay, in any case it’s better than saying outputs twice, then at least that can save you time, exactly the other will have been even longer,, but typically, if If you have conditions where the two branches are calm and full,, then you can actually always save yourself by simply taking that from the front and somehow ordering it from the so don’t exactly expect everything that we say,. But those are things that you you should also look at it so that you can program better and shorter later.

A

Well. The next step was this: next step, really wonderful. First, the functional signature. Many of you started to hand over a vector from google. You then noticed at the latest that the test didn't work out that assumed in the test that something like this could be transferred. But why would you rather transfer something like this? Instead of a vector from louis.

A

Yes, that means less complex.

A

Not the data itself, not the data itself, the reference yes, but not the data itself, but not for the first time like this right. If you go down this path, if you want to, then you say yes, I want to have ownership of this sector in rast. You have to say you always take with the guy lehmann explicitly what you want to do with these guys, and if you say that here then you say me would like to be different from these flights, so I would like to be able to do everything with it.

A

It's not true. We only need to read. Do you want to accept what is sufficient for us? We just want to read something and then, when we first write this and before that, that means, when first of all, just take one in the youtube fans on this way, but why not that? But the especially live? Yes,.

A

Right here in the test, for example, that 's just something is created here directly. That means this rey is not allocated to the hip. What the vector to example always makes. Sometimes you want to put airways in there or some other stuff and not just vectors, just as flexible easy. So we agree. It needs to be returned, of course, but also an editor, because we can't return a reference to something we just created. So here it is again the same game in the city.

A

We know that from the old way gate now we go through all of them and had to search out the indices down to the last detail. That is a bit more difficult because you have to take these boundary conditions into account. You can either do it with modolo or you can do it with modolo, so make the alexis on the right even easier. We just act +1, but then make the sounds modolo. If it happens to have been the last, then it's set to one again for the other.

A

It's a bit more difficult because you first have to add the length and then 1 and then again modolo the length, but the logic behind it is the same: the problem is, for example, in rast. What is that? What do you think what that is? There are.

A

Somehow only a few possibilities that you can imagine here once that's one and that's maybe four or 4.

A

First, isn't what you think it would work, just try it out.

A

A

Yes,, it stays with 1 1. That means that's why we have to do this old length, but you can take a look again and there it will be it's just that, this time an animal corresponds exactly to exor. That means you can tell these two, so the two neighboring cells from the previous step simply ex ears. You don't have to worry so much about it. It would, of course, also have been nice if you had written that out explicitly.

A

Let's get up I'll, do it now, because your update got to know the match, you could say now and leading index, then fetch the current index and the leading index I'll write these three parts. Now an opel be three double now I can be pretty nice about it. People by I just say what happened, then. That's what I have somehow, because these eight cases have to be worked. Through, of course, I always somehow 1 ended so that all through workers, then you somehow get through it, yes,.

C

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A nested management, oh so, oh.

A

No,, so that you, if you have to say goodbye a bit,, especially with rast, the source code, you write corresponds to that which comes out later. That is. I have already mentioned that I gave a lecture about performance and I will address it later after reading it, but the compiler makes so many optimizations. The compiler is pretty much everything to do with you. Wo n't recognize your source code anymore. When you look at what the compiler makes of it,, so I would say you don't have to worry about that at all.

A

The compiler makes some major optimization anyway So. If we have these two options, a now and yours,, then the compiler can convert between them without any problems and decide for himself what and who knows, that is always better than for humans, make it.

A

Explicit that we were also quite nice to use the match features or you can now also take the simplification here and is extra, then only the 1 here I only have a function definition in the mail, but then I have a rich one here now code first I read the old state, then I use this helper function, the recipient state prints out to press the beginning part and then I just go through lampions that by the way you can make a constant.

A

Somehow nice change at the top gentlemen goes through it for a long time, says always nextstep, because she closed the because you stayed and then pressed in. You stayed and then I know that yes,.

A

The in the water.

A

Whether you also in the crowd.

A

Oh, so meant meant that one would write here that something like that would actually work, but afterwards you can no longer access it. So once it is created here, it is given in the function cleanstate rhein, but then it is gone, not quite well, so exactly that we have the commandment. So there are questions about it.

A

Just like that pokémon, I hope such things should now be clear to everyone that the tutors of this event are too masculine, and I pay per month. It didn't even notice, because I just told you they used to play pokémon or still here, clearly no question. He ok, at least most of those who are sitting here right now. Ok are going normally row free through the first thing, I think was the print pokémon is not always like that, and it's still quite simple.

A

We have here again only one before loop adorn that through the pokédex through and then that's probably he's thinking about your next to the pokemon that are in there, I.e. me assume. You've all got your head pretty much ready for the tasks. That's why I won't explain everything that pokédex defines below keep it up and that's the joke here.

A

I said it wasn't particularly important that it was right, but if you always want three digits to be spread out and filled with 0 in front,, then you can do it that way or you can actually omit it, I saw that these are just these special actions that you can enter there in this format. You can find all of that somehow in the documentation of sd mmc, which often also briefly quietly also just opened up. You haven't visited your face.

A

Yes, that also wanted to set up should definitely set up what I said at the beginning with the search engine. This whole description is quite long, but you would actually see it here at the beginning of this example. Here we can do it with leading you. So there is a lot you can do there. You would definitely have found it as soon as it was clear, somehow people what funny I'm not sure what that is.

A

I understand yes, but you definitely want.

A

That next was, I think, next time, this function here it's supposed to find a pokémon with a given name in the pokédex. But what happens now? If you don't have a pokémon with the name found in java, you would give a return, but we don't have that. So let's do this one option return. It was only mentioned very briefly at the end, but we actually do that here and here there are two options for how to in the whole program. So you can proceed somehow.

A

I decided to always return this pokémon model by reference, but it was just as right to simply return it directly that we were okay too, but if you decided on the reference, then you had to with many functions here this static extra to say this reference is always alive. Disco codex was defined down there as a constant. That means always alive. It lives in the executive.

A

So, no matter how you did it, but with the reference you have to specify the statics, which I also send by e mail or at least posted up the one to the other is pretty much the same. So like ritalin through the pokédex, by always comparing the name of the book, one we got and if we found that read early return returns on the model. Important we have to prescribe on now model is not just a model, is now not an option.

A

It is not like in java that we can always just write the type directly or no. No, we have to explicitly say this is also an option, and then we have to say we either have sun or we have then, when this loop comes, of course,, then the land is returned,.

A

Then you come this year,. You look, I also said that there is a model, somehow, here, I took the reference again,, but you could have saved it directly,. Then there is it all. First of all, the pokémon has the actual current stats of this pokémon and the level for which, of course, we only need eight. The designer function.

A

A

That I ca n't answer that directly now, what's not the reason that the franc is, I know not what I look at directly again. Look there ask a tutor. Maybe okay then definitely have this. This construct, this paste function, this pokémon model names and level and then falls back delivers. You just have to always call these functions to get the to get the current status.

A

Then there is this series of perpetrators who are not so very special, and then there is this function here this day of july, this parameter can be transferred, and here you can also use this ratings up again, which I presented last time. This will be complete here, good at it and you accordingly, one of course, with this function a tectonic. We know from the monster from the lecture questions about this about these types. It.

D

A

Yes, the first parameter of these parameters, especially there are three versions not in the on youtube as eleven in the youtube as eleven and in the consumption in the self which we don't have. That would be here, but you always have to look like just with the parameters. What do you want to do with this guy? In most cases, we only want to read, so it has to be that it has to go here. If we only want to read it has to go there.

A

If we also want to change, then it has to go there and in very rare cases, if we want to consume it, that is really rare. We write that we are looking for a trainer. There are only these three cases of what actually only two very very often, questions about the type.

A

You are just the other methods to write a little bit. Annoying are, for example, pokémon. How do you return a pokémon model directly to you so no longer an option, because we simply repair as long as one so have we go using this guessed string method. Compare that with question mark. If the question mark is then we press this list, and then here I think, has been a bit of a problem.

A

Terror is as this fine pokémon call bynames and it's unclear what to do with it then do exactly that and you will get an options back. That is a the normal way to deal with them is to use a match and split it up and go through all the options. What options do we have with option with option? We only have the option together and if it's a fan, then it sticks even more to it. Then there's more data to it. These data weep. We have the name profile, and then we hear this problem.

A

That's an early delivery, but if the case arises that it's a landing, then you just press only something out and then nothing happens here anymore. But all of this is repeated again in a magnifying glass. That's.

A

A

A

If you can, if you have some awesome funny conditions here, then the compiler can't find out or don't know if this loop ever comes to an end, and if the computer can't prove that you'll never get here, then the compiler says then please give something back here too.

A

So you mean okay, you can, of course, do that by simply saying pokédex 0 or something else that, of course, very much ugly. Actually, yes, you don't want that exactly so that the compiler knows that there is something similar down there. Yes and the rest is good. I think there was so much interesting with. I will just upload it to you like everything or anyway, then you can upload it look at the same thing exactly what happened there. I think that nothing was too interesting.

A

Anymore? Why? Because tormented you read the error message. Someone else had.

E

E

A

So, ok, if you don't do this check this tree yourself, berlin, the year after next, quite well, what your problem As far as I'm, concerned, I, don't know exactly what you mean, so I could n't imagine what panic could occur with them.

A

Also lead to few positive, but let 's talk about it right away that the task is nice and long. We can continue now so.

A

A little welcome, I've noticed my mistakes. Fortunately already and I would like to refer this link in particular, because I learned a lot from it. A.

D

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Long blog article about error.

D

A

D

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Wrote to the blog article also helped with an operating system that was developed in a language that was also newly developed, specifically for the operating system. More or less, and this huge team has been working on it for a very long time before game errors can make an offer of this new language and the.

C

Beautiful explains.

A

What you actually have to consider when troubleshooting, what is finally important for error, handling bike, & programming languages, so I take out a lot of information before I start right now there is a small preliminary course, so to speak, the Let's briefly talk about function, contracts, if.

B

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Function,, so we know our friend, who we can also simply omit as forest,, so we want a function. Disk normally changes the vector, so takes a youtube as 11 and normalizes this sector, of course,, it's only possible now.

A

If this sector, not the 0 vector, is a way to normalize for anyone who hasn't heard linear, algebra or anything else called bringing it to length 1, you can do this simply by dividing all the components through this longer part which is longer, but only if that are 1 0 vector is so we can't divide by the longer. So this function only makes sense. If we're not talking about the new rector and that's what this function conference is for, that it's not a language feature, but something you actually always have just what you disregarded.

A

So there are mainly two components that are important: that the tri conditions- these are the things that must be the choice before we call this function. These are prerequisites to the world that the function works properly. Now the conditions are about saying what happened next is, for example,, that the post condition here is that the longer before this sector after that is 1 and as I said, that it has nothing to do with what you see,, but it is not English or anything else. You always have off when he programs only off that.

A

Maybe no one is quite there with you, but you always have to think about it. I have certain prerequisites for the world so that my function works at all, because other examples that come to your mind.

A

E

Let's say the division is assumed to be exactly right.

A

To do the same thing, we have a division that must not only be one of the parameters, my project of any function, that has a condition before we can call. It example. The.

B

Miner search what.

A

Kind of condition does it have if we want to carry out a teaching search.

A

On an rwe or something else, not that anymore should be sorted and you are looking for. That is a complicated condition. We have there. Yes and, for example, some mathematical functions is whether germany would. There are of course, also functions, no critical data at all.

A

For example, a print function takes every string that is somehow valid, and small ones could freeze from it no post at tables important that not specifically, that has nothing to do with java c++, but you always have that when you program I, think I introduce one more so that you question whether the animal has already been doing this the whole time.

A

But what I want to see how we deal with it now I would like to set a small task, and that is: let's categorize mistakes present a few mistakes, and later we differentiate between categorize 0.

A

That means, if we have against the leader and want your that start, there is a year, for example, new protection fell back then we have a configuration file that we want to redeem from programs and has an invalid format because it is somehow damaged or the user has done. It wrong we initiate an rwe or also build an index for easter. We want open a file, but.

D

A

Find it on the file system, we have his contract, long smiles. That means called functions, but do n't meet all the requirements for the function. For example, we book enormous live with a lector. We want to return with a server rina doesn't answer, so we can't solve the website under data. We are. We have no memory left on our pc spread out 0, we couldn't find a key management and the user entered a few letters instead of a phone number.

A

I want to give you a little time. Now, feel free to do so too. To talk to your row or neighbors. We want to divide them into two categories. One tries to find out how you would part there for the present time.

A

Who thinks they have a rough idea who thinks they have an idea? After all, you are already written here. I say: please write another error on the left or right.

A

Or is there at least one that contradicts.

C

A

Right complex what you just learned, so if I just think, if I somehow normalize my 0 vector, do you believe what concretely, what do you think or right.

F

Now that we're going.

A

To describe that, why did you decide to do it? You were now pretty much of the same opinion. It seems to me that I want to write up here now. How would you describe these types of snagging mistakes that imagine that.

D

On the left, there are more mistakes that are caused by the programming itself, so it's during the complete time and on the right. It's just errors that are from the outside. If the file that should already be called up does n't exist, it just does n't work or if the wrong input.

A

Someone says something to others: what to add: how exactly is bastian quite good, so that are the courier brothers that are not what speaks a functionally before tense, often of the world. If you somehow address something player archipelago so that men in the state device state of the world is broken for us,.

A

Right there are the limits a bit exciting. Sometimes that is pretty clear. It is often but not accessible, so strongly wrong. Data is read in beach. Instead, I hope that pretty much everyone agrees that somehow, through this world, what we are out here and another page 0 dlf that probably happens through new users ravens. I think too definitely count as one you said, the contract creations. I would also count in any case the programmer has now also called this function. The programmer is to blame.

A

If no one else is right, there is a bit of a discussion and in fact I would say that, with the crash strange now, everyone write explain why and olaf manthey on the left side, all of memories, but just exactly what is pretty much in the middle. There is a bit of arguing about it. That's why it works quite well. I made the setting, for he should with the collision. I just said.

C

C

C

A

A

C

C

A

More or less, if you of course, actually give the user the possibility to run the calculator directly, so to speak, you give the user the possibility to run the source code directly. If you have a pocket, calculator then sit down divided directly to one divided by. That means you give the user the possibility to execute code. The same way you could argue with contracts nation if you now have a sine function or otherwise a bad example.

A

If we have a root function and the user and we put the wide calculator of the users if there is a negative number,, it is also the fault of the user, right,. But of course, we first have to somehow read in the user input, and it is our task to validate it, so that we then later pass this input on to this function,. That is our error,. A programming error,, I.e. the programming error, is the fact that we did n't check the user information, but jan is a bit difficult to understand. At the beginning,.

A

Exactly with the phone number makes a lot more sense that it somehow has to be intercepted that he does n't say any nonsense, but has to do it that way, you catch that when you share only what you divide by zero does not mean what the user enters directly, but what you do yourself with your algorithm. Yes, that is the focus on it now speak more precisely. What this error, how we categorize it want an error that has not yet said, but that.

D

A

An important difference we expect here we have to expect from the world more precisely valid user input, in any case also the money, maybe a bit unclear. We have to expect that china, I'm not there is. Actually we have to do that. In most cases, we have to wait until a china is possible that we just have to see if there is more in there beforehand. The other four sides are clear: the other things are unexpected. We actually never expect us to get away from these things that shouldn't happen.

A

We don't want to call up any program. Advise let's see if there's a differentiation between 0, somehow that results can that you want him to the reason, for the first is an invalid state of the world. That told me that's somehow, all of on the outside, what affects all the inputs are growing. They are invalid and the program has to because the program has to reckon with what can handle it happening, so they can be.

B

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They must also be treated as expected and the others come from the reason that the program- it's not the world- that's invalid,, it's our program, that's invalid, and in particular, we can act. Almost on love here is out of memory. It's actually so easy to stand out where you think autonomy. I could treat it now.

A

You can half imagine it away, because actually you could treat out of mary, but in most programs it makes no sense to treat it yourself if you write an operating system. Of course, you have to deal with it. Somehow, if you write very,, very low level drivers or something else clearly, then you have to deal with it and calculate with it.

A

What most programs don't make sense to count on is to count on the fact that autonomy no speak, we're there, like that and first of all, now recovery out so from which we can, where we can catch ourselves again and the other end of bugs, because these are errors in themselves and now, let's go through how we would treat these errors first, the bucks again as a reminder they are unexpected and especially not treatable. In the vast majority of cases, the program could do everything afterwards.

A

If we had somehow referenced the memory in Wertingen, if we had ray read out or if we once differentiated, 0 or divided by 0 using nails, the status of the program somehow unpredictable beer king, knowing that the program will do next when the program obviously.

D

Couldn't handle.

A

The situation right now, so we don't know whether the program somehow behaves in a good way when wanting to keep the weather going that 's important just to accept or understand. Why? That's that clear, that classes of bugs ca, n't handle they're unexpected, and we can't take it for granted that the program then did the.

E

Right thing that.

A

I would n't now that 's, of course, also a bug how you normally use the word. But it's not. This bug invest my page 9 in a correctly implemented. Algorithm is definitely a valid program. What you wrote there, that is not doing what it promises for people, but.

E

Such a valid lot, according.

A

To our current definition of growing here, hear me say something about other things: later,, for example. If you had installed something on the wrong prima, but according.

D

To the current definition.

A

Of bugs coming from africa, that would be ok, it wouldn't be an error.

A

B

Said now we don't expect the error.

A

We can't handle it and the program could do something else. What is the solution, then? What do we want to do if there is an error like that.

F

A

Program- and that is actually quite radical for some or for many when you hear it for the first time,, but when you think about it,. Yes, we absolutely want to end these people's blog entry. That's just me canceling everything and in particular we want to cancel. Everything could already be infected so where the program could already have done something that means if we divide by 0, want to write the result somewhere, then we can already have influenced others. If you somehow just cancel one function now, but another function will use the result of it.

A

Then then this virus spreads further, that everything could be in a strange status then spreads out. That means we want to have it sort of under quarantine and everything that somehow touches can tear off together and that can be processor. The web. That's a bit difficult processes are natural, larger than and processes have even less possibility to communicate, somehow worse things with other processes. What is it, but so that we calculate the tredup with panic?

A

That's why you've already seen panic since I would recommend you to do it again at home to think, because it's important that you accept that you accept that we actually cancel because, but certainly.

B

Because now almost.

A

No corner is simply something we can do and we can describe it directly with this market. We will explicitly want to penken. So me I panicked, and then this happened here. You've probably seen it before and that's because it's on, then you get a little hint and yes, then it was over with the program or with the street, but since we didn't have any more nor any additional have created, switzerland is around everything wakes up 1. Then you have a lot to see again in which other situation as more exact car manufacturer excuse, asked.

A

First of all, you can hand over this panic, marco other things that works. The reason we thank everyone hand over more information. If we, let's do it with eyes of the car builder. If you do this here, for example,, it's obviously dismantle when it first combine that the computer of both looks you'd rather tell us that it's going to be combined and as promised, it then happens. Luckily, so that's exactly what we're doing what.

D

We are going to.

B

A

Now it depends directly and.

B

It always says you.

A

Have to respect race for vectrix, so give it a try. If you have this place again and then under.

B

Linux, I think the same.

A

For me that you just asbeck, grace equal to 1 and then the file finds then comes.

B

A

We mostly work out like this, and sometimes it helps in this case it does n't really help, but sometimes life helps to see which function. So in things refer to it, it can also come from java. If an exception comes here, then you always have his way to the call count. That's somehow, if you see a few panics, then you can, there could be a little more the banks how it could be and a little hint what penken does that's doing an action called all my thing is not that important for you.

A

I will explain it briefly anyway, so that once it is clarified, if a program is perfect somewhere deep in a function, then it clears the whole stack. Panic does not immediately end the program, so obviously there is something else, but even then it turns to the program immediately, but first the ass.tec is cleaned up. That means, if panic is triggered, the trust is raised tuesday. So now we have several function tests there. We go down the path we see going deeper and deeper.

A

When I am completely call a lot of functions, then rast climbs up the stack again until all rehearsals until maine functions and for him with each of these functions, job trust shop. All local variables is the expression of hatred for the structures for the displays have or finally ice cream for the yamaha and just fine lets just much less powerful more about that later, and that will definitely be tidied up now that you can release various things,, e.g.

A

memory or close any sockets or close files or end other transactions, things that definitely have to be ended or close a database connection. That would be quite good if all this happened. You might think that it is not absolutely necessary. Then, when I finish the program there is the g1 walter frey operating system and also network sockets or files are, he was closed by the operating system, but there are definitely found what you also in the end. You have to do what is important.

A

If you now play with the bank again, for example,, where a transaction has to be carried out,, then it should be atomic that you transfer it from one account to the other, and then it will be canceled me enormously.

A

F

A

With this job methods that we will.

F

Discuss later because.

A

You can write yourself what still has to happen. Yes, that usually costs a lot of time, because the whole way has to be gone up and all these drop functions have to be called and that’s it for us anyway, pretty important. He pretty unimportant, because the program or the network process ends anyway afterwards, but you can.

B

Also deactivate it if.

A

You see or want it at some point, then you can say that panic is a simple board. That means yes, it doesn't matter it just stops immediately. If, but you usually don't that you background information area is n't that important for you at first,, which is why we didn't appear about it in europe. A few people would have just said: it,, e.g. the indexing of rays or rectors. If you specify an invalid index, then bad things happen,, namely panic. If you made one behind the operation, this is my overflow or each other flow happens.

A

Then panic man there are but a few other possibilities have you experienced any other panic times that would cause me to stand.

B

E

A

Right about this option compare there can, but it also happens if we omit them. Nobody else has seen other triggers.

A

There are a few special ones you have to use that you can use eg accept with marco. That's basically just a marco which calls panic directly panic with a message. This function has been added, not implemented or something like that,. You can write where you would expect a value,.

A

So if you return a function to the typing service ring and the faction wanted to write it now but couldn't write, it then write to panic at the moment,. That's just too running time, of course,, that's very unpleasant. You do n't want to do it all the time, but every now and then it makes sense that in any case, it makes sense this time before, what's even a penny, so we don't do anything special they're just called differently. So you know, what's meant a revival is called says.

A

This part of the code will never be reached. If we just did this example with the main loop, we had complicated conditions in it, but who comes. Unfortunately, I can prove that this condition, if it breaks off or something else, then we have to prescribe the motto with the compiler. Happy is, and doesn't say, enke, but still had to fix something or a service like that. You've probably seen that before and didn't really pay attention. If the test failed, it's a failure.

A

Are those stars that I wrote in there that somehow check, but that is the same or if something is true, the soers also just call panic if they are false. This can be used in particular to check these contract value relations too.

A

So, if we paint this and earlier, we better pass it because it just better to the same, be under 100 or under equal to 100. I saw it different possibilities saw some of you just ignored it. It happens, some of you actually did. It will hear look what did or did anything other than what was right. You would in the method, in the description when writing this function. You will describe that. You have this concept that you have the practical ones. The level must be less than 100, and then you just say panic.

A

If that's not true that, we may have noticed that this context is not a loss of language, I'm speaking about that, has nothing to do with weed we're, not going anywhere truck contract or anything else. For us. No key words for that's just that. It's that you describe it in the documentation of the method that you then ensure it yourself, for example, popular with others, I, for example, blogs,. There are all such things,, and even if we later work with result and whether they work,.

A

The 3 you can use yourself,, so in any case, the other two are not quite over,. You could use them yourself,. He can take a look. Are there any questions about these bugs for your first class.

A

Ok, then, each time via recovery, we do it in other languages. Who remembers? How do we do it? We act bugs in the year was correct.

A

With the exception it was correct, but does anyone know what more precisely they will be direct conclusion right exactly? There are two types of.

C

Exception: nine years years.

A

There are six sessions that always have to be noted explicitly because the function that throws- and there is this runtime exception that can always be thrown without the function signature having to notice anything about it and actually, if you still remember, everything in vw, already talked about these two classes from out in succession. These are in this check sessions for the world errors that you expect and for everyone else. There are these edge amex options java actually has them too. Already these two classes procedure errors somehow recognized. How do you do it in very precisely?

A

Are checked exception, ten years we do. The sc has someone programmed c here: okay,.

A

A

Was often short with arrow as a previous proven one usually or often at least one just gives it back back and saying if it was zero, everything went well if it was 1 or something went wrong because of another number.

A

Here is an example that you can see now, so everyone who didn’t want to be confused by htc can also look directly or something, but here it has its ried function. Then you often do it in such a way that you save in the return value. We are in the workflow, either 0 for everything, okay or something else, and the actual return here is made using so-called parameters. You simply have a friend who has this function? If, you don't write it in anyway,.

A

You can't surround yourself with several things,, so you can't surround yourself with types like that with titles that make my csu almost exactly that,, but you can see you're already calling this function, here,, too, oops, that comes back to the internet,. We just take that into account not at all and don't make any errors now. No error handling renovating is simply a very simple goal to forget that, but basically there are these two categories of error handling in all languages.

A

There are exceptions or something about return, values, and also new languages, accompanying others always pick different things: many scripting languages, or dynamic languages, often use exceptions and other new language on pusher evaluation. There are very interesting concepts but little surprised and what uses on return values and no exception, but what makes that a bit different than in cee, because then you can have it for sure. We already know these two types up to old and young.

A

We might take a closer look, but that's better than error codes, because it's somehow difficult to ignore these errors. You'll have noticed that if you get an option like that, you can't just do it do it as if you got a real object. You.

D

Ca n't just ignore it.

A

That an option is not the right object. You have to somehow unpack the right results from the also quickly shares from the ream. That means he can always do something manually and could do n't just ignore it,, for example, more in here, and we now expect this open. A a free comes back. A freestyle tvo that happened. Ok ag is free, but then there are also options that are unrealistic. Now there is.

D

A

This variable part of the method that also want to call a arrow is defined. Then it doesn't work because that's a must here. First of all, an error could have occurred. Then we just don't have any valid, no valid files at hand. The questions about this.

A

But you've probably already seen that they're simply an option got back, for example, from pokemon, and you couldn't go that far with the option to do as not do exactly what the pokemon could have done.

A

My biggest example helps the definition we will use of free the file in the city, library.

B

A

Different so say that this on function and so would be a stream and slice passed. Then one comes back old or ok, so it 's filing and who isn't ok worth a screen and then in other functions, promise to remind.

D

A

Seems what defines it like that? It was a weird thing. We only got to know each other for a short time last week, but these inner ones are just a display of different possibilities. That means it can be kay or he can be in there with possibilities from dire dawa cherix, but I hope that is quite clear to you. What is meant by that when we here actually time from self so have file and string.

A

That means my ok value where an arrow can sit in it, an error value where a strict sit can sit in it and we do what.

B

I just showed that is not.

A

Possible just call arrow up, but now there is a lot of the type of salt and stream, so just don't call up this result. It on has no method wide was, of course defined in file.

A

Yes, that does n't work, how to actually open it first, we save that, for example, is an anagram variable again, that is of the type divides, file string and a person more about it, always if in you has that means, even if the result or option have you first want people to just go through all the different possibilities: possibility 1 and then you want Finding a name for what's in there.

A

I know that requires some kind of experience that you slowly figure out how it works with these. But since we said here that extra data depends on an ok case and extra data is incurred, we can also use this data, say it like that, and now we've got the name, this extra data there are the last three goals say what you always wanted to do.

A

The second case is that would have terror, and now we find this lamey on the string of data. This name is with the types. This is more of the type stream on which we can use the same, for example, to make an output and then output the string again, that's even so far and I do n't think that's quite a.

A

No, that depends as.

C

A

Depends on the say here with an arrow and string. That's about the typical. We can also have time here from 5 and 32 more then you would be 32.

C

A

Sound entirely convincing I do.

B

A

Have to you can also say it if I just like that, a lot assume that the rx are clear. So if we say something wrong, you 32 can either do that. Ok, you hit.

A

32 first, don't all are offset the example to show alexander that you with whom he has.

C

Two other types: what.

A

Is he state stabilized? That means all types are always clear to live moment, the compiler. That means you have to somehow specify which type of error returns just like when you write normal function, check, celebrate or anything else that just admits this error just says, is the file so.

C

C

C

C

C

A

This function can now define that can define what types there are and what it does in this case, so it is open, it is in there, for example, is felix is and if it doesn't exist now, for example, there is return, error 5 what would be in a bad case or give back pensions spring? What is a bit better, with higher error solemnly found, we will give.

B

You a bit further the.

A

File, the right.

E

One here everything is.

A

More difficult, if you want to participate a lot, is it flies after equality? A bit nicer opponent.

E

A

Is a blog that you look at, you have to be recognizable, so if you were in the match, was my block.

A

F

F

F

A

But, first of all completely different case: not what the whole thing will work, but what happens or what we should do does n’t work for us In the event of an error,. We now have a function that we want to write ourselves,, namely copy file,. We give a path beginning at the source and entering before the destination and which is to be copied. In. They were now programming ourselves and now.

A

Dare the file managers want the file first open to read the data in is the data the data in and then want to write it out again in the other file that is happening here now. So we have ok file, ok, fall, then we would do everything else that we actually intend to do here is a small comment. Yes, somehow already two levels indented that ugly and in particular the question what you actually have here in the case of inheritance.

A

Yes, that is the question you have to ask yourself and the most had simply nice ignoring years. You would always.

B

Have it like that nice.

A

You always just say I did n't really want that, and I just carry on what are they actually not good? What you want to do now inform about this incident, so just nothing to do, then you can call this method or this copy file function and nothing happens, and when it was called you ask yourself why not that just happened ignoring it is very bad. Printing. The error is also very bad. For the most part you do n't want to find an error in every function. You want to tell the user about very few functions.

A

You want you, don't download any library now something different if you use such a rektor from the standard library, you also don't want any of the methods to output anything from the terminal. If something goes wrong, because the rektor would output me all new by the way it didn't want to be on the terminal, we wanted a few functions that were output to a user and if you wrote a function like that, you did n't want to go directly into the panic.

A

It's also a bad idea, because that means we don't treat the error at all say so as if we didn't expect the error, but we have to deal with the error in any case, because it can of course be that the file doesn't exist. So you shouldn't do the three things.

A

If now very very rarely, that means handing the error up that what we already know from exception and to do this, we have to rewrite the function signature a bit, then it is now itself a results operated before we didn't return anything and now a large part is going back. But since we did n't return anything before it's okay, who is from now gives then it would make sense to give everything worked. We just want to say that everything worked, but additional data can.

D

A

Added to it, but if.

B

A

Didn't work then, of course it makes sense to give additional information and then give this string further. We will already get this urgent error message from Pfeil open then I.

D

E

A

But no additional data I think other.

B

Things too, so that's important.

A

We have to change this return type, but this match this case now. Just say: okay, here that 's, not ours problem, we just go up, read more string now say error again. That means manchester is now the last expression in the whole function. That means what is returned in the individual. People is returned from the function and here in.

B

A

Ok case, we would of course, still do some things. I have now abbreviated, but we will admit at the end of this thing, an ok with these weird double doubles because we somehow have to give back a year. Why just tell me always a large part back, be it here too, the writers have to say it explicitly: it's okay, but we'll write somewhere, because nothing sensible can be green. It's.

A

Important that you have to change a return type, that's different than in years, for example, that wouldn't be known. Yet in java you can just throw an exception like he's funny, since something everywhere, the mechanism of the return is going to be touched explicitly, and here again the note we want to report errors to the user in very upper functions,. So, for example, we couldn't do that because we.

B

A

In the stack, if we've already called many functions, that.

B

That's one possibility.

A

Give that up again, but sometimes you can actually deal with the error directly. That was also seen in the top man task. I have this okay, you do n't have to have looked at that, but maybe you have already provided use for this song. It's a blues, one from the user. Now you would think where you are amazed. There is no or no optical return. We still have to assume that the user enters nonsense important, but this function, acts directly and with this I have just shown yes enough.

A

That ensures that for so long continues to run so far. If the user has actually specified something valid, then we have similar string and gas here, and so this kring sat once whether the really integer use it ok comes back then return. We say that immediately otherwise, or do it again, and the loop continues to run this short.

A

We're only doing this here because we can just keep asking questions, but that's not always possible. Actually, it's rarely really so in fewer cases than half that's possible to treat the error directly on site.

A

Post another one here, little awesome, now error handled, look forward to you at the beginning. I can fix the error right here on site and place. That is rarely the case, but if that is the case, then you can do it. Here is easy, so you can try again or use similar default values if it So it's. Okay, if you have to enter something there,, but if that's not valid, then some standard should be selected or something you usually do.

A

N't have that there and then you ask yourself: am I very high up,, for example the mail or just a level like that under the name there I can tell the user directly that it went wrong. Then I say somehow, okay, so I think that either but by making pop, even if I write a graphical interface, but that is.

B

Rather, the rare.

A

Incident, usually, you are always deep in it, and there are enough with the error further above, in which we change the youtube and instead of giving back the direct plan during a stop. Somehow we know we already have that, because the problem is the clutch exactly that we are indented here. 2 levels and before this ok returned is the end of the functions when doing things and if.

B

A

Always gave two people to the right: whenever we got a tear stop, then they would come rather faster. This 100 character limit necessarily not my idea how we solve that.

F

A

That sounds tempting to write a function for it. The problem is so there will be this function, so in the end, I think I would stone that if.

D

You wrote that I would just give this function. Salt.

A

E

A

Is that some people think that people will match latics the same blablabla writes, then you can also give something back and again had this first level get yourself. Basically only you said now in the event of an error you give a meaningful, is.

C

The full back exactly.

A

Right you give them. What you want to do in this case were after above is enough realiter. That means we just have. A mistake are like that. Lets.

B

A

First and then this whole match the expression and the ok case. We just go back the part but give it back to the experts what you end up with in the other case, so it is only the early return. What he has already seen differently makes sense that.

A

You can, of course, do this as often as you like. If we want to open the others, then he can do it like this. We already have two open files on the first level and can then work now just finish the topic. It was for a short way, guys want to return medium at all the wheel, already string so far a complained and yes strings. Maybe not the best idea now has with the string as an error type where the description can be in it, but you.

B

C

C

A

Exactly if I want to deal with the office, which will be the case in most cases, it is not given to the user immediately. Then it is difficult and now open the file. I want to do other things if it says celebration not found or if it means. If me I, have a right to this. File, I might want.

B

A

Other things and I ca n't tell the difference. If a string could return, so I have to know exactly what's in the string and pick up this error, and maybe someone changes the string later and then I have to I'm. Looking for keywords like this in the sprint to find out if what's happening, right now is definitely a bad idea.. A. Better idea here is to use them with an error that can occur and then somehow write methods that can make a string out of that.

A

You have a few errors: errors of a string during the entire winter break.

A

The turin can be empty, then the streaming can be invalid character. So if after adel arises, then if yes, it could be hexadecimal, but let's say it's in there, then I can't do that as integer phases. This sounds, then. This error case occurs and its surface stringer can be a very small number that does not fit into my integer that you realize for the first time that these are the main error sources that can happen,, I.e. the main error category can never happen if I enter a to drink from it.

A

An internal one he would like a functional means suitable where one takes a ring and then gives one back, and that would be ok. This resize is the 32, because that is what I would like to have in the end and then the case is the pass Endeavor and not bring, and now we have, for example, another method write for the passport holder who supplies an art to because we then actually want to give our drinking water back to the users to say to each other that the input was wrong or something.

A

But if we did don't want to show users directly, then of course it's better. If we simply know people.

B

A

This sienna, instead of being searched for by strings.

A

A special case there's a special part, of course, even if the.

D

A

Type should be wide, then it goes back because it's already accurate that if there is no additional information together, but just an optional okay, I'm almost at the end. There are questions about the slides about china. Then there's then, first that we make a bit of a title here, but a little bit and this hennig and match history to understand a bit better and next time would start a larger program which I will now do live, which I will then do live customers where we will think a little bit about how best to design.

A

We will build the president pocket calculator. That will also be part of an exercise. That means when you don't need to, you're bored on wednesday world,. It's best not to officially publish the exercise tomorrow, because.

D

A

Explain the code in a lecture, which is good until wednesday.