SBT is a build tool for Scala and Java projects that uses a Scala DSL for build definitions. It has conventions similar to Maven and allows simple projects to be set up easily, while also supporting more complex builds defined using Scala code. SBT build files can take several forms, including simple .sbt files or Scala files in a project subdirectory. Keys in SBT are scoped and can be configured differently based on the scope, such as for different modules or tasks like compiling documentation.

1. SBT <<= (Build) { FTW }
@indrajitr

2. SBT
• Build tool on Scala for building Scala-Java projects
• Compliant with Maven's convention (mostly)
• Basics done right
• Easy to set up for simple projects (intrusive)
• Shares a *lot* with Scala
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

3. Build Definitions
• Simple: Quick DSL
• Diabolical: Scala code (with embedded DSL)
• And the shell rocks
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

4. Build Definitions
<base>/*.sbt
<base>/project/*.scala
<base>/project/plugins.sbt
<base>/project/plugins/*.(scala|sbt)
~/.sbt/plugins/*.(scala|sbt)
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

5. build.sbt
organization := "net.liftweb"
name := "lift-demo"
version := "1.0"
scalaVersion := "2.9.1"
libraryDependencies ++=
Seq("net.liftweb" %% "lift-webkit" % "2.4-M4",
"org.eclipse.jetty" % "jetty-webapp" % "7.3.0.v20110203" % "jetty")
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

6. project/build.scala
import sbt._
object LiftBuild extends Build {
lazy val projects: Seq[ProjectReference] = Seq(common, actor, json)
lazy val framework = Project("lift-framework", file(".")).aggregate(projects)
lazy val common = Project(“lift-common”, file(“core/common”)).settings(/*...*/)
lazy val actor = Project(“lift-actor”, file(“core/actor”)).dependsOn(common).settings(/*...*/)
lazy val json = Project("lift-json", file("core/json")) dependsOn(common % "test")
//lazy val foo = Project("lift-foo", file("core/foo"), delegates = common :: Nil)
}
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

7. The Expression
Reminder:
Statement ≠ Expression
Statement:
val foo = bar + baz
Expression:
bar + baz
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

8. The Expression
The expression:
organization <<= organization or normalizedName.identity
Is a: Project.Setting[S]
And <<= is thus:
final def <<= (app: Initialize[S]): Setting[S]
for: InputKey, SettingsKey
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

9. The Emojis
The ONE
<<=
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

10. The Emojis
And the rest
:= += ++= <+= <++= ~=
• Initialize ( := )
• Append ( += ++= <+= <++= )
• Update ( ~= )
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

11. Scoped Keys
sealed trait Key[T] extends Scoped
final class SettingKey[T] extends Key[T] with ScopedSetting[T]
final class TaskKey[T] extends Key[T] with ScopedTask[T]
final class InputKey[T] extends Key[InputTask[T]] with ScopedInput[T]
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

12. Examples
name := "lift-demo"
name ~= formalize
resolvers in GlobalScope += JavaNet2Repository
scalacOptions ++= Seq("-encoding", "UTF-8")
resolvers <++= isSnapshot { s => if (s) Seq(ScalaToolsSnapshots) else Nil }
inceptionYear <<= inceptionYear ?? Some(2011)
organization <<= organization or normalizedName.identity
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

13. Examples
libraryDependencies <<= (libraryDependencies, scalaVersion) apply { (ld, sv) =>
ld :+ scalap(sv) })
libraryDependencies <+= (scalaVersion)(scalap)
libraryDependencies <+= scalaVersion apply scalap
scalacOptions /*in GlobalScope*/ in doc <++= (name in doc, version in doc) map
(Seq("-doc-title", _, "-doc-version", _))
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

14. Settings are Scoped!
def in(s: Scope): Result // ScopedSetting, ScopedTask, ScopedInput
def in(p: Reference): Result
def in(t: Scoped): Result
def in(c: ConfigKey): Result
def in(c: ConfigKey, t: Scoped): Result
def in(p: Reference, c: ConfigKey): Result
def in(p: Reference, t: Scoped): Result
def in(p: Reference, c: ConfigKey, t: Scoped): Result
def in(p: ScopeAxis[Reference], c: ScopeAxis[ConfigKey], t: ScopeAxis[AttributeKey[_]]): Result
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

15. Miscellaneous
MOAR Emojis (in shell)!
~ + ++ ; ! < -
Plugin, State, Life, Universe and everything else
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

16. Lost?
Befriend ‘em
• Defaults.scala
• Keys.scala
• IDE
Bay Area Scala Enthusiasts Meeting #42 (10-10-11)

17. Exercise

18. Questions?