When comparing Ceylon vs Xtend, the Slant community recommends Ceylon for most people. In the question“What are the best languages that run on the JVM?” Ceylon is ranked 4th while Xtend is ranked 7th. The most important reason people chose Ceylon is:
The compiler prevents you from using a potentially null variable, unless you check it is not null. Ie. it forces you to check a potentially null value before using it. The type system is strict, but flexible, allowing union and intersection of types, covariant and contravariant types, reified types, etc. Type inference and union types allows a dynamic programming style, close of JS spirit.
Ranked in these QuestionsQuestion Ranking
Pro Strong static typing, null safe and flexible, almost dynamic type system
The compiler prevents you from using a potentially null variable, unless you check it is not null. Ie. it forces you to check a potentially null value before using it.
The type system is strict, but flexible, allowing union and intersection of types, covariant and contravariant types, reified types, etc.
Type inference and union types allows a dynamic programming style, close of JS spirit.
It brings type safety to JS, allowing to define interfaces to existing JS APIs, yet using the
dynamic keyword for flexible calls in the JS ecosystem.
Pro Excellent IDE support
Ceylon has reified generics, so it doesn't loose the type of collections at runtime. This makes autocompletion, debugging, etc. first-class. The Eclipse plugin makes it a full-fledged Ceylon IDE, and an IntelliJ IDEA plugin is in the works.
Pro Great tutorial
Gavin King, main author of the language, has a great, clear technical writing style, making understandable difficult concepts like variance or sound type system.
Pro Try it out in the browser
It has a Web IDE: http://try.ceylon-lang.org/ with impressive demos: http://try.ceylon-lang.org/?gist=bd41b47f325b6d32514a so you can try it without installing anything, and see the JS generation / interop in action.
Pro Excellent documentation
The language specification is very complete and up to date; also, the language module is very well documented.
Pro Easy to learn even if you don't have prior programming experience
Ceylon is indeed fairly easy and readable. Of course those ones who know OOP and a bit of functional programming concepts will feel almost at home right from the start.
Pro Generate HTML
HTML generation is supported right in the SDK.
Pro Same code in backend and frontend
Pro Ruby-like syntactic conveniences
Lambdas are written like Smalltalk's blocks. If it's the last argument, it can go after the parentheses like Ruby's blocks. Parentheses on method calls are optional.
Pro Type inference
It uses Java's static type system, but you don't have to declare the type of everything all the time, since the Xtend compiler can usually figure it out. This also dramatically cuts down on Java's infamous verbosity.
Pro Code runs just as fast as Java
Because Xtend relies heavily on JDK and Android classes, it runs just as fast as native Java code.
Pro Easy to switch back to Java
Xtend is a low-risk option. Because it compiles to human-readable Java, if you decide you don't like it for your project, you can just switch back to Java without losing your work.
Pro Extend even library classes with new methods
This is where it gets its name. You can open classes and add new methods, kind of like Ruby. (Of course this has to be compiled to Java, so really it lives in a kind of helper class.)
Uses functional features ,which are very concise and idiomatic. Plus it has annotations, which cuts down on the Java boilerplate.
Pro Better defaults than Java
Methods are public if you don't specify, and fields are private. Locals declared with
val in Xtend are
final in Java. This dramatically cuts down on Java's infamous verbosity.
Con Lack of physical or electronic books
We should hope Red Hat or anyone interested would take the time and write one. That would strengthen the maturity of the language, but Ceylon is rapidly developing which can make the author's efforts futile because his or hers work will become obsolete soon.
The second hindrance is, of course, popularity of the language which can't give much to the pockets of the author (however, Dart's unpopularity at start didn't prevent it to have a lot of printed material, but that's Google's child, we know).
Con Currently has large runtime
Ceylon 1.2 needs a language runtime of 1.55 MiB, and the Collection library adds another 370 KiB. That's a lot for the Web...
Now, this has to be put in perspective: if you use Ceylon to make a web application, these files will be loaded once, then cached by the browser (that's not casual browsing).
Moreover, most servers compress such resource, and the numbers become respectively 234 KiB and 54 KiB, which is more reasonable...
Con Difficult to configure in Android Studio
Con Slower compilation
Unlike most JVM languages, Xtend compiles to Java rather than directly to JVM bytecode. So you have to compile everything four times for Android: from Xtend to Java, from Java to JVM bytecode (.class files), from .class to .dex bytecode, and then AOT compilation from .dex to native ARM upon installation. This can really slow down development and testing vs a more interactive language like Clojure.