README.md

non-nullable-fields

This library adds null-check assertions to class definitions to ensure that class fields do not contain nulls. This may be desirable when using Java libraries or Spark.

Quick start

Add the following to to your build.sbt file -

libraryDependencies += "io.github.michaelt293" %% "non-nullable-fields" % "0.1"

For scala versions 2.11 and 2.12, enable the macro paradise compiler plug-in -

addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)

For scala 2.13, use the -Ymacro-annotations compiler flag.

Example usage

To add null-check assertions to class definitions, use the nonNullableFields annotation macro.

import io.github.michaelt293.nonNullableFields

@nonNullableFields
case class Person(name: String, age: Int, numberOfPets: Option[Int])

If null-check assertions are not required for optional fields, set the ignoreOptionalFields parameter to true.

@nonNullableFields(ignoreOptionalFields = true)
case class Person(name: String, age: Int, numberOfPets: Option[Int])

The nonNullableFields annotation macro can also be used on implicit classes.

@nonNullableFields
implicit class StringOps(private val str: String) {
  def clean: String = str.filter(_.isLetterOrDigit)
}

Macro expansion

At compile time, the macro annotations above generate the following code. Note, a null-check assertion is not required for the age field since Int is a value class and therefore cannot be null.

case class Person(name: String, age: Int, numberOfPets: Option[Int]) {
  assert(name.!=(null), "Field, name, from Person cannot be null");
  assert(numberOfPets.!=(null), "Field, numberOfPets, from Person cannot be null")
}

case class Person(name: String, age: Int, numberOfPets: Option[Int]) {
  assert(name.!=(null), "Field, name, from Person cannot be null")
}

implicit class StringOps(private val str: String) {
  assert(str.!=(null), "Field, str, from StringOps cannot be null");
  def clean: String = str.filter(((x$1) => x$1.isLetterOrDigit))
}