- Former Cons
IntroductionI have been promoting Scala for quite some time now, and I have encouraged all of the developers in my office to try it out, hoping that at some point we can start using it for new projects.
It was suggested to me that I put together a list of the pros and cons of Scala to help other people in the company evaluate whether they should consider using it for their projects. After pondering this I realized that this would likely be of interest to a wider audience than just at my company, and that it would make a good topic for my blog. Thus this post in which I list what I believe to be the most important factors that a company that wants to stay on the JVM platform should consider when deciding whether or not to move from Java to Scala.
Because this comparison is specifically Scala versus Java, I do not include the fact that Scala runs on the JVM, has performance on par with Java, interoperates easily with Java and after compiling is essentially indistinguihsable from Java. While these might be benefits for some companies when comparing Scala against other language such as Ruby or Python or other JVM languages, they do not distinguish Scala from Java.
The intended audience for this post is not the developers who might be using Scala, but the technical managers who are involved in the decision about what technology to use. I don't discuss Scala's cool features such as closures and continuations, easy interoperation with legacy Java code, traits with code, or a sophisticated type system with type inference, but focus instead on the business-level questions of how using Scala rather than Java might affect the success of a project, a team, or the company.
My company has not yet produced a product using Scala, so my experience is limited to some prototypes at the office and some personal work at home. The points below are based on that experience plus my interpretation of comments from others that I have read in the last couple of years. Everyone's viewpoint differs, so you may disagree with my statements or my evaluation of their importance. Similarly, the specifics of your situation may make your experience with Scala significantly different than mine. It is easy to find both praise and dismissal of Scala on the 'net. As they say, YMMV.
Higher ProductivityStudies and anecdotal evidence indicate that Scala programs are from 1/2 to 1/10 the number of lines of code as compared to a functionally equivalent Java program The larger the application, the more apparent this difference becomes. If you believe, as I do, that a given programmer can produce roughly the same number of lines of code per day independent of the language used, you can see how this reduction of lines of code can translate into a substantial increase in productivity and a faster time-to-market.
Higher QualityScala encourages a functional programming style, which in turn leads to code with fewer bugs. Also, fewer lines of code means fewer bugs. Fewer bugs means higher productivity and a higher quality product.
Scala's Actor library and its encouragement of immutable variables help to avoid race conditions among multiple threads and thus improve reliability in concurrent applications.
Better DevelopersProgrammers who learn Scala pick up programming practices such as functional programming that they can (at least to some extent) apply to other languages, such as Java. This makes them better Java programmers. Providing an environment in which developers can learn something new should also make for a more positive environment for those developers, so they will be happier with their jobs and less likely to leave the company. Likewise, a shop that uses a new and advanced language such as Scala is more likely to attract top-notch developers (which Paul Graham has named as "The Python Paradox").
Rapidly Improving EcosystemThe early adopters of Scala such as Twitter are well down that road. Here at the end of 2010 it is tempting to say that the early adopter window is closed and anyone who starts with Scala in 2011 or later is no longer in that category.
Some of the cons listed below may never change, or change very slowly, but at least the tools issue will certainly improve. The rate of improvement of the Scala ecosystem is much faster than most other languages at the moment. The IDE tools are improving, the testing tools are improving, the documentation is improving, and the functionality of available libraries is improving. All of these improvements will continue to make the Scala ecosystem more attractive over time. If you evaluate the current situation and find it close to satisfactory, and the problem areas are the ones that will improve with time, then you probably won't have to wait very long for that to happen.
Learning CurveScala incorporates features and concepts that are not familiar to many programmers, such as functional programming and continuations. It can take some time to learn these concepts. Some people say the Scala syntax is more complicated than Java, but in fact the language spec for Scala is significantly smaller (191 pages) than the language spec for Java (684 pages). The difference is that Scala is much more regular and allows things to be combined in ways that can't be done in Java, which provides more power and expressiveness but also can take some time to learn.
I have seen comments to the effect that it could take about two months for a Java developer to come up to speed on Scala, although a developer who already has experience using other languages with functional constructs such as Python or Ruby should be able to pick it up faster.
Limited Developer PoolThere are far fewer developers who already know Scala than who already know Java, which means it will be more difficult if you need to staff up quickly and don't want to spend any time training.
Because of the more advanced concepts embodied in Scala, or at least concepts which are different from the concepts that many Java developers have internalized, it may be possible that some Java developers will have a difficult time coming up to speed on Scala. This would effectively decrease the overall pool of available developers even if you are willing to spend the time to train someone on Scala.
Until a much larger number of current Java developers try to learn Scala it will be difficult to know how much of a problem this will be. One possibility is that many current Java developers will not want to put the effort into learning the new concepts required to use Scala effectively, and that a large chunk of the growth in the pool of Scala developers will come from new developers who were educated with those concepts from the start.
Better DevelopersWait, wasn't this listed as a pro for Scala? Yes, this one is a two-edged sword. Even after accepting the Learning Curve and the current Limited Developer Pool, there is a possibility that not every Java developer has what it takes to become an effective Scala developer. Scala provides tools that allow highly competent developers to write very concise code, and if you give them those tools they will use them. Developers who are less competent may then have trouble understanding that code. Java suffers less from this particular problem because it doesn't provide the kinds of high-level constructs (such as higher-order functions and continuations) that can cause difficulty for less capable developers. If you take the Scala road and hire highly capable developers, you may be making a commitment to continue to hire only highly capable developers for some time.
You should ask yourself this question: would your company culture allow you to hire and keep a developer who is twice as expensive and ten times as productive? If your answer is "probably not", then you should stick with Java where you can hire those developers who are half as expensive and one-tenth as productive.
Limited Commercial SupportIf you have a large Java project and you find you quickly need some additional developers, you can call a consulting company such as Accenture or Cognizant and they can throw an army of Java developers your way. If your project is written in Scala, I suspect they will happily tell you they can provide you with those resources, but they might have more difficulty doing that due to the above-mentioned Limited Developer Pool.
You could probably post a request to the Scala or Lift mailing lists and find some contractors with Scala experience to help you out, but there is not yet much in the way of explicit commercial support for Scala.
The recently founded company Scala Solutions is the first I am aware of that is advertising support for Scala in mission-critical applications. Large companies considering Scala may not be comfortable without having more choice here.
Tool ImmaturityThe development tools for Scala are not as advanced as for Java. In particular, the IDE plugins are not yet as sophisticated, so developers who use IDEs may encounter some frustration. On the other hand, this issue should be addressed by Scala's Rapidly Improving Ecosystem.
Former ConsWhile browsing the web you may run across people complaining about the items listed in this section. As I note for each item, as of this posting at the end of 2010 I believe these issues have been resolved.
Risk of Breaking ChangesAs a new and evolving language, Scala has gone through some breaking changes a few times as new versions have been released. This has caused a lot of pain for some people, a number of whom have declared in their blog posts that this demonstrates that Scala is just an academic language and not ready for the real world. I believe that, while there still may be some changes to be made, with the release of version 2.8 the language has reached a level of stability that makes it suitable for production use.
Risk of AbandonmentScala is a relatively new language, and some people feel that it may not "make it" and survive as an ongoing language, in which case any code written in Scala would become hard to maintain. I believe this risk is now relatively small, given how it has been growing over the last few years and the number of big names who have adopted Scala (see the list below).
Limited DocumentationWhile this may still be an issue for non-English teams, I believe there are now enough Scala books in English that this is no longer an issue for anyone who reads English. The Books on Scala page lists 19 books about Scala and Lift, including five Scala books in English and five in other languages (some of which are translations of the English versions) that are currently available.
Web Sites using ScalaThe Scala web site has a page on Scala in the Enterprise, last updated a couple of months ago (as of this posting), listing quite a few companies that are using Scala.
Here are a few well-known web sites using Scala or Scala/Lift and some tech articles about them:
Other PostsThere are a fair number of posts listing technical pros and cons of Scala, or comparing Scala to various other languages such as Clojure or the others mentioned above, but it is more difficult to find commentary that is more specifically directed at the business or management questions. Below are links to some posts that, while often containing some technical content, also contain at least some more general comments. The posts are listed from newest to oldest.
- A thread from September 2010 asking if there is a place for management to get support on Scala decisions.
- Some comments from August 2010 on looking for Scala developers (vs Java or Python).
- "Why is Scala so fashionable?" from July 2010 - mostly comments about the Scala technology, but a few others. David Pollack says Scala "lives up to its hype" and has a great community.
- "Why Scala" from May 2010, a 15 slide "Executive Overview", although the first half is all technical.
- "Is this the time to switch to scala?" from January 2010 - Geir Hedemarks blog entry in which he takes a step back and asks why a company might be asking if it is time to switch to Scala (as opposed to asking some other questions). (In July 2010 he accepted a job managing a group of Scala developers.)
- "Why Your Company Should Let You Use Scala at Work", January 2010 blog post by Graham Lea discussing switching from Java to Scala.
- "A Scala Success Story" from September 2009 about Capital IQ; mostly technical.
- "What is stopping you from switching (from Java) to Scala?", stackoverflow poll from September 2009.
- "Why should I switch to Scala?", August 2009 post with both technical and some business-related concerns.
Updated 2010-12-22: removed "Higher Performance" item per James Iry's comment, fixed Foursquare per harryh's comment.