Scala interview questions
pedrorijo.com
pedrorijo.com
1. I can NOT off the cuff answer those all correctly (at least not without a little Googling).
2. I can, largely off the cuff, implement an IO monad in Scala using higher-kinded types and compose instances of them in a hand rolled non-blocking server.
The state of interviews in tech is, for the most part, abysmal. You either end up with language trivia which tells you nothing about somebody's ability to reason about good solutions to problems or you end up with some contrived white-board problems that simply show you the candidate spent a decent amount of time on leetcode/careercup/etc and nothing about their coding style, design choices, etc.
I've found that the best compromise is a two layered approach. Offer a straightforward collaborative coding question or hackerrank test to weed out anyone that's clearly incapable of writing code. Then have them complete a short project that you discuss with them at the onsite interview. Make sure the project requires a nice number of data structures, etc. You can really grill them about design choices, tradeoffs, what-ifs, etc. In my experience, it becomes immediately obvious if they know what they're talking about. Sure, it's extra work for a candidate. But in my experience anyone that actually wants to work there seems to prefer it over fast-paced whiteboarding.
I remember two interview experiences at "big 4" tech companies where I was given two fairly involved algorithmic problems and only 30 minutes where I proceeded to write as fast as I could and finish with only minutes to spare, despite knowing exactly what to do. Then I was grilled about SFINAE in C++. The whole experience left a very sour taste in my mouth, despite the nice comp they offered.
When you have your 10th interview with someone applying for a senior front-end job and they can't tell you how many columns are in Bootstrap, when Bootstrap is on their resume and they made a point to bring it up in the interview, it makes you question humanity. Unfortunately this is why you end up with questions like "What is the difference between `unapply` and `apply`?" or "How many columns are there in the Bootstrap grid?"
And unfortunately, especially in my geographic area, the majority of work is done as an employee or a consultant under an NDA. Nobody is bringing a GitHub profile with a solid green commit graph, nobody is coming with 45k rep on SO, and nobody is coming with years of blogging content we can look at. That's not necessarily a problem, especially if you've ever been in the same room as someone who is very proud of how many SO points they have, but it certainly complicates interviewing.
So when you have a combination of (A) people who lie through their teeth to get a job they are in no way qualified for; and (B) people with no public technical profile to speak of, you end up with interviews full of trivia to make sure they have a pulse and contrived whiteboard coding to make sure they can understand the fundamentals. This is doubly hard if you're trying to respect people's time and limit interviews to a brief phone screen + a 60-minute onsite interview. Some of the suggestions I've seen here about take-home projects, consulting work, coming into the office for 2 paid weeks, or a 3-day long interview bonanza, are insulting.
Be a little flexible; not everyone finds the same things "insulting".
It seems to me that you'd at least have to forego most of the grilling bit - explaining why I made the design choice of using a list instead of a set (or the other way around), and what the tradeoffs and what-ifs are is just a roundabout way of asking "what is the difference between a set and list?" -- and if that's what you really want to know, skip the project and just ask that.
But remember, Scala can be written in many ways. Some of us write Scala like Haskell-lite, and others write it like Java with less cruft.
With that said, I'm not sure if these questions are actually useful:
(1) They're pretty basic. Any good programmer could get up to speed with all these aspects of Scala in a week, possibly less. So you're not gaining anything by filtering candidates based on whether they already know this. In fact, you're wasting valuable interview time asking very low-value questions.
(2) If you really do need a Scala expert, these questions can't identify such a person.
How are code review with people like that? Where they implement their own logging system rather than using built in tools. That must be truly enlightening. Must be fun to maintain too. Especially when they do not understand or can even use the built in functionality of a language.
I think it's very telling that you think THIS of all things is the issue with interviews.
It was also not my point at all that an engineer that knows how to build a construct like an IO monad in Scala, but doesn't understand traits/abstract classes (which would be funny and hard to find I imagine) would be preferable to anyone else...
And furthermore, I agree that we live in a world where teams and projects get hosed by architect astronauts. But that isn't the point either...
The point, my angry friend, is nothing more than the observation that I, with my skill set, would do exactly what I said: Be unable to answer all those correctly in an interview, and in the process I would not have been asked anything that would flesh out many of the other skills I have. Skills relevant to the language in question and, arguably, more empowering to an organization than those listed.
> Level A2: Intermediate application programmer
> [...]
> - XML literals
I'm sorry; I really want to like novel languages, strongly typed language, portable languages, and a bunch of other boxes that scala does check. But stuff like this... what?
This may be my most reddit-worthy comment in the history of Hacker News, but sometimes you see a spade, and you just have to call it a spade. Scala has the most utterly bizarre priorities.
A tool to check that my XML is valid: great! Yes, please! Great; but that's not a language's job.
Write a tool for it and invoke it in another step in your build process. Call it a linter because that's what it is: a linter is a process that checks other documents for correctness.
Type inference for a language and XML grammar checking don't belong in the same process; they just don't. Only sadness and wasted (human, and machine alike) time can come of it.
This is from 2011, and in any case represents knowledge of Scala as it is, not Scala's priorities. In 2012, Odersky, discussing Scala's priorities going forward, pointed to XML literals as a language feature to ax for Scala 3, moving XML handling to libraries.
https://groups.google.com/forum/m/#!topic/scala-language/PV4...
Which is too bad, in my opinion, as HTML is mostly XML, too, and they are immensely useful for HTML templates in Scala.js environment (like React's JSX on steroids). Who'd have guessed.
I can only hope that thanks to the amazing work of Eugene Burmako, we'll have SQL literals, JSON literals, and whatever else, all properly typed, of course. Now _that_ would be something!
lazy val x = {
println("computing x")
3
}
do {...} while ((line = file.read()) != 0)
this post was never a "memorize this and you will know scala" statement, or that if you know those answers you will get a scala job. I simply found those questions a while ago and decided to provide answers by myself as an exercise. I do believe some answers may not be completely right (even completely wrong), and others may be a starter for a nice and productive discussion.
Also, knowing the answer to these questions doesn't make someone a good/better developer. These are just some small islands on the (scala) software developer knowledge!
In my opinion these are somehow basic concepts (that will only be valuable when applicable on 'real life' code), and there is a lot more to explore, specially about the type system. To know more about the type system have a look at this awesome article I found: http://ktoso.github.io/scala-types-of-types/
Unfortunately, these are questions often done in several scala-related job interviews (I had my share. Coincidence or not, I never accepted an offer from a company which did that kind of questions) :(
Feel free to provide feedback or discuss some topics.
Thanks!