SBT: build.sbt, Dependencies & the Shell

SBT is the most widely-used build tool for Scala projects -- handling compilation, dependency management, testing, and packaging, roughly analogous to Maven or Gradle for Java. Notably, build.sbt is written in actual Scala syntax, not a separate configuration language.

build.sbt & Dependencies

name := "my-app"
version := "1.0"
scalaVersion := "2.13.10"

libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.15" % Test

// %% appends the project's Scala BINARY VERSION automatically
// (resolves to scalatest_2.13) -- since Scala libraries are often
// published as separate artifacts per Scala version

// % Test scopes this dependency to testing only -- not bundled
// into the actual shipped production artifact

The Interactive Shell

sbt
# Enters an interactive session -- run multiple commands without
# restarting the JVM for each one, avoiding real per-command startup cost
> compile
> test
> run

# Watch mode: automatically re-runs a command when source files change
> ~test

Pinning the SBT Version Itself

# project/build.properties
sbt.version=1.9.6

# Ensures every developer and CI use the same SBT version,
# regardless of what's installed globally on a given machine

Incremental Compilation

Rather than recompiling an entire large codebase after every small change, SBT analyzes exactly which files changed (and what depends on them) and recompiles only that genuinely-affected subset -- meaningfully faster iterative development on larger projects.