Getting started

The calculator runs inside your build tool. Add the plugin, run one command, read the number. Nothing is uploaded and no source leaves the machine.

sbt

Add the plugin to project/plugins.sbt:

addSbtPlugin("dev.constructive" % "sbt-cardinality" % "0.0.6")

sbt 1.10 and later use the same line: sbt selects the sbt 1 artifact (sbt-cardinality_2.12_1.0). Then run:

sbt cardinalityReport

sbt cardinalityReport measures every definition the project's Compile sources introduce — nested definitions included — and logs a report. The same report is written to target/cardinality/report.txt (cardinalityReportFile), so a build can keep it, diff it, or post it as an artifact.

scala-cardinality — 1 source, 10 definitions
  stored-value estimates: constructor inputs only; finite capacities are upper bounds
  ?: unresolved, not a proof of infinity
  2 unresolved · 4 with more than one value · 2 with one value · 2 abstract
Stored-value estimates (constructor inputs; `?` = unresolved)

?  example.Holder[A]  class     Light.scala:11  unresolved: A
ω  example.Succ       class     Light.scala:17
ω  example.Timeline   class     Light.scala:19
2  example.Custom     class     Light.scala:5
1  example.Zero       object    Light.scala:16
—  example.Light      abstract  Light.scala:3

cardinalityReportSelected analyzes named signatures only:

sbt 'cardinalityReportSelected example.Accessor.get'

cardinalityReportOf runs the same report over sources the build does not compile itself — a directory, a single file, or a published -sources.jar:

sbt 'cardinalityReportOf path/to/sources.jar'

Mill

For Mill 1.3 or later, load the plugin in build.mill's header and mix CardinalityModule into a ScalaModule:

//| mvnDeps: ["dev.constructive::mill-cardinality_mill1:0.0.6"]
import millcardinality.CardinalityModule

object foo extends ScalaModule with CardinalityModule { def scalaVersion = "3.9.0" }

mill foo.cardinalityReport, mill foo.cardinalityReportOf <path>... and mill foo.cardinalityReportSelected <qualified-method-name>... run the reports; each writes report.txt under the command's out/ directory.

The calculator alone

"dev.constructive" %% "scala-cardinality" % "0.0.6"

The build tool may run on JDK 17, 21 or 25. The calculator reads dependencies compiled by Scala up to the version its TASTy reader supports: 0.0.5 and later read Scala 3.0 through 3.10. A newer Scala's jars appear as dependency stub not read: … TASTy signature has wrong version at the end of the report.

Next

Reading a report explains the rows, the tiers and the moves that lower a number. Assumptions states what every count assumes.