Scala traits that override toString to display parameter labels
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Labeled ToString

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The Labeled ToString project provides several traits you can mix into case classes in order to get toString representations that include parameter labels. That means you get Person(name=John Doe,age=30) instead of Person(John Doe,30).

API Docs (ScalaDocs)


Here's a normal case class:

case class Person(name: String, age: Int)
Person("John Doe", 30).toString
//result is "Person(John Doe,30)"

Here's our labeled case class:

import com.yuvimasory.tostring._
case class Person(name: String, age: Int) extends LabeledToStringDef
Person("John Doe", 30).toString
//result is  "Person(name=John Doe,age=30)"


labeled-tostring is hosted on Maven Central. You can add it as a dependency to your build.sbt file. It is built for Scala 2.8.0 through 2.9.2.

libraryDependencies += "com.yuvimasory" %% "labeled-tostring" % "0.5.0"

Choosing a trait

The com.yuvimasory.tostring package provides three traits: LabeledToStringDef, LabeledToStringVal, and LabeledToStringLazyVal. They override the default case class's toString method with a def, val, and lazy val, respectively.

  • If you're not sure which to use, start with LabeledToStringDef, which works in all cases.
  • Consider LabeledToStringVal if you know the case class's parameters are either immutable (e.g., primitive types, immutable collections), or have string representations that never change (e.g., arrays).
  • Try LabeledToStringLazyVal if you meet the criteria for LabeledToStringVal and want lazy initialization.
  • Both of the *Val traits may run toString much faster after the first call, since the store the result. The cost is a bit of memory and a slow initial toString call.
  • You must use LabeledToStringDef if your case classes are Squeryl tables. If you don't Squeryl will generate bogus SQL.


Benchmarks are in a separate repository.

Object creation

[info]                          benchmark      ns linear runtime
[info]              CreateCaseClassPerson    6.66 =
[info]     CreateLabeledToStringValPerson 1262.54 ==============================
[info] CreateLabeledToStringLazyValPerson    8.68 =
[info]     CreateLabeledToStringDefPerson    6.63 =

First toString call

We don't have a good way to benchmark this presently.

Subsequent toString calls

[info]                                         benchmark   ns linear runtime
[info]              SubsequentToStringsOfCaseClassPerson  750 ========
[info]     SubsequentToStringsOfLabeledToStringValPerson  146 =
[info] SubsequentToStringsOfLabeledToStringLazyValPerson  185 ==
[info]     SubsequentToStringsOfLabeledToStringDefPerson 2594 ==============================


  • These traits produce unexpected strings in the REPL due to the way the REPL wraps code and mangles names.
  • These traits do not work if you add bodies to your case classes (i.e., additional methods or fields).