How we write and use Scala libraries not to cry

About me

• Name: Toshiyuki Takahashi
• Working at M3,inc.
• Twitter: @tototoshi
• Github: github.com/tototoshi
• #rpscala

M3,inc.

M3,inc.

M3 & Scala

• Unfiltered
• Scalatra
• Playframework

M3 & Scala

• seratch/scalikejdbc
• t2v/play20-auth
• t2v/holidays
• t2v/stackable-controller
• tototoshi/lift-json-play-module
• tototoshi/play-json4s
• tototoshi/scala-csv
• tototoshi/play-joda-routes-binder
• tototoshi/play-ascii-art-plugin

Lots of libraries

• useful!
• but ...

Three Problems in Scala

• Compilation time
• Binary Compatibility
• Ecosystem

Theme 1

Binary Compatibility

In Java

<dependency>
  <groupId>org.mod4j.org.apache.commons</groupId>
  <artifactId>lang</artifactId>
  <version>2.1.0</version>
</dependency>
        

In Scala

<dependency>
  <groupId>com.github.seratch</groupId>
  <artifactId>scalikejdbc_2.9.1</artifactId>
  <version>1.4.3</version>
</dependency>
            

Binary Compatibility

Prevents us from fast migration to newer version of Scala until all libraries our products depends on supports newer version.

Be careful!

Binary Compatibility

• Can't use libararies build against Scala 2.9.2 in Scala 2.10.0.
• Can't use libararies build against Scala 2.8.2 in Scala 2.9.2.
• Can use libararies build against Scala 2.9.1 in Scala 2.9.2.
• ...(´д`) ...confusing

SBT

Cross Compiling

crossScalaVersions := Seq("2.9.1", "2.9.2", "2.10.0")
            

> + compile
> + publish
            

Source Dependencies

import sbt._, sbt.Keys._
object ScalaProjectBuild extends Build {
  lazy val scalaProject = Project(
    id = "scala-project",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      // add other settings here
    )
  ).dependsOn(
    uri("git://github.com/tototoshi/scala-csv.git#0.7.0")
  )
}
            

Scala Binary Version New!!

from SBT 0.12

ArtifactId now includes not Scala version but Scala binary version.

<dependency>
  <groupId>com.github.seratch</groupId>
  <artifactId>scalikejdbc_2.9.1</artifactId>
  <version>1.4.3</version>
</dependency>
            

<dependency>
  <groupId>com.github.seratch</groupId>
  <artifactId>scalikejdbc_2.10</artifactId>
  <version>1.4.3</version>
</dependency>
            

Scala 2.10.x ensures their binary compatibility

During RC period

Before 2.9.x

Scala version == Scala binary version

Theme 2

Library Hosting

Library Hosting

One upon a time

• A major repository for Scala libraries until earlier 2012.

Now, Sonatype

Why should we use sonatype?

• cloned to Maven central
• It doesn't require resolver settings in your build.sbt
• can't remove from Maven central.
• Sonatype has resources to ensure things are working (not volunteer)

Conclusion

• Be careful to binary compatibility.
• Be careful to dependencies of your products.
• SBT 0.12 introduced Scala binary version (Upgrade your SBT !!)
• Push your libraries to Sonatype

Enjoy Scala!