Comments on: Scala Goodness: Compound Types

By: Pooria

Pooria — Fri, 01 Jan 2010 22:55:56 +0000

“Think of Traits like interfaces in Java with implementation code.”

That makes me think of abstract classes in C++ with implementation code!

By: stephan

stephan — Thu, 31 Dec 2009 07:31:51 +0000

@Dimitirs: “… continuous marketing can result in more mindshare, so, thanks :)”

Thought the same about continuous marketing.

By: Yardena

Yardena — Thu, 31 Dec 2009 06:56:41 +0000

@Dimitris you don’t necessarily need a value of a type to make it useful. Nothing is a very useful type :-) Seriously though – sometimes you just need to express a certain constraint for the compiler to check. Take a look at HTMap – you put 5 and “hello” into it, get an HTMap[Int with String] and then obtain 5 from it with get[Int] and “hello” with get[String].

By: Dimitris Andreou

Dimitris Andreou — Thu, 31 Dec 2009 03:19:03 +0000

@Yardena, “String with Integer” is a type with no values, pretty much useless, which makes it a poor example :)

@Dirk, the types define allowable collaborations. So what do you feel is missing?

@stephan, I wanted to see a “Scala Goodness” blog for some weeks now – since I was seeing “Groovy Goodness” floating around, and continuous marketing can result in more mindshare, so, thanks :)

By: Viktor Klang

Viktor Klang — Thu, 31 Dec 2009 00:23:03 +0000

Dirk: You can, with self-type declarations

By: Random Links #102 | YASDW - yet another software developer weblog

Random Links #102 | YASDW - yet another software developer weblog — Wed, 30 Dec 2009 22:20:37 +0000

[...] Scala Goodness: Compound Types Ja, Scala ist auf jeden Fall einen genauen Blick wert … [...]

By: Dirk Riehle

Dirk Riehle — Wed, 30 Dec 2009 18:35:14 +0000

I only wished Scala didn’t only support roles/traits but also first-class collaborations. The action is in the interaction of the roles, not in the class interface combining the roles.

By: Yardena

Yardena — Wed, 30 Dec 2009 16:53:29 +0000

@Stephan – great post on indeed very useful Scala feature.
@Daniel – you are right, but in Java the support for compound types is very limited. Compound types can only be used in generic methods, they can only compose of interface types (and java.lang.Object for erasure tricks), and they don’t support type parameters. While Java’s conservative approach is understandable, in Scala, you can really go wild and define types like “String with Integer” or “T with S” and even do something useful with it, like the HTMap (http://github.com/dlwh/scalanlp-core/blob/master/src/main/scala/scalanlp/collection/immutable/HTMap.scala)

By: stephan

stephan — Wed, 30 Dec 2009 16:19:10 +0000

@Daniel: Excellent, thx, helps me with current code!

By: Daniel Spiewak

Daniel Spiewak — Wed, 30 Dec 2009 15:46:55 +0000

Strictly speaking, Java supports “compound types” as well, at least in the example you gave of the method parameter requiring two interfaces:

public void callAndFeed(T cf) {
cf.call();
cf.feed();
}