Scala advantages after Java having closures

Apart from closures (which Java doesn't appear all that close to having), here's a list of features in Scala that are missing from Java. I'll omit libraries here and concentrate on the features of the language itself. This is not comprehensive by any means, but I think it contains the big ticket items.

Implicit parameters / conversions
Pattern matching, case classes
Type inferencing (some)
Higher-kinded types (abstraction over type constructors)
Monadic for comprehensions
Variance annotations
Interfaces with behavior (traits)
Default and named arguments
Unified methods and operators (methods can be used as infix operators, operators can be overloaded because they're just methods)
Unified type hierarchy; no primitive types
Properties rather than getters and setters
Abstract values
First-class immutable references (vals are as easy to declare as vars)
By-name (lazy) terms (maybe Java closures would make this reasonably easy to express)
Some tail-call recursion optimization
Abstract types
Type aliasing
Self types
Path-dependent types
Structural types
Type ascription, as distinguished from type casting
Renaming imports
First-class modules (objects)
First-class packages
Reified generics (manifests)
Delimited continuations

Some cool secondary constructs that these building blocks enable:

Type classes (via implicit parameters and higher-kinded types)
The "Pimp My Library" pattern (via implicit conversions)
Internal DSLs (via operator overloading and infix methods)
Parser combinators (enabled by higher-order functions and made pretty by infix methods)
Generators, coroutines, custom control structures (via delimited continuations)
Type-level programming (via higher-kinded and abstract types)
Obsolescence of dependency injection frameworks (via the Cake Pattern)

Lastly, I'll mention that Scala has a REPL (read-evaluate-print-loop)--not really a feature of the language itself, but it's very nice to have!

I'd disagree on the Collections library part, Scala's Collections are created with Scala in mind, Java's with Java so naturally they're different in a lot of ways but they're still both excellent, patern matching and traits however are something that're really missing from Java.

Esko 2010-10-02 07:51:23

Java's collections library was implemented without any thought towards immutable data structures. This is a mistake in any language.

pelotom 2010-10-02 09:19:07

@pelotom: Java doesn't have inherently immutable data structures at all so I don't think truly immutable collections in Java won't show up for a long while. I'd venture a guess though that what you're referring to isn't a *de facto* thing for a language, it's more of a feature used by certain kind of programmers which of course isn't a bad nor ignorable thing.

Esko 2010-10-02 21:19:55

@Esko: I'm not sure what you mean. It's perfectly possible to define "inherently immutable data structures" in Java, the collections library just neglected to.

pelotom 2010-10-02 22:01:06

@pelotom: `final` in Java isn't same as const which means you can break it with reflection, you can't declare programmatically that your class is (deeply) immutable, Java itself doesn't support easy constructs for fast copying of objects... Nope, immutability isn't a feature Java does natively, you can get very close with clever programming (*see `String` class as en example*) but it's still not entirely immutable.

Esko 2010-10-03 07:44:26

Quite a list. +1.

fastcodejava 2010-10-02 09:57:22

Great list, and because I can't see something like this without trying to add to it, here are some additions to consider: abstract values, abstract types, duck-typing, first class modules (objects), obsolesence of dependency injection frameworks (via cake pattern)

Dave Griffith 2010-10-02 12:22:23

Good additions, I knew I was bound to forget some important ones!

pelotom 2010-10-02 19:18:14

Another one : the ability to precisely choose the visibility of classes, leveraging the hierarchical nature of packages. I miss that a lot in Java.

barjak 2010-10-02 20:21:48

It may be useful to explain that "operator overloading" and "methods as infix operators" come from the same design choice : the fact that operators and methods are unified.

barjak 2010-10-02 20:29:16

Thanks @barjak, I incorporated your suggestions.

pelotom 2010-10-02 20:49:53

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Scala advantages after Java having closures

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