bplommer / diffx

Pretty diffs for scala case classes

diffx

Pretty diffs for case classes.

The library is published for Scala 2.12 and 2.13.

Scalatest integration

To use with scalatest, add the following dependency:

"com.softwaremill.diffx" %% "diffx-scalatest" % "0.2.0"

Then, extend the com.softwaremill.diffx.scalatest.DiffMatcher trait or import com.softwaremill.diffx.scalatest.DiffMatcher._. After that you will be able to use syntax such as:

left should matchTo(right)

Giving you nice error messages:

Using directly

Add the following dependency:

"com.softwaremill.diffx" %% "diffx-core" % "0.2.0"

Then call:

import com.softwaremill.diffx.Diff

//import this or extend the trait with the same name
import com.softwaremill.diffx.DiffInstances._

Diff[T].diff(o1, o2)

Customization

If you'd like to implement custom matching logic for the given type, create an implicit Diff instance for that type, and make sure it's in scope when any any Diff instances depending on that type are created.

Ignoring

Fields can be excluded from comparision by calling the ignore method on the Diff instance. Since Diff instances are immutable, the ignore method creates a copy of the instance with modified logic. You can use this instance explicitly. If you still would like to use it implicitly, you first need to summon the instance of the Diff typeclass using the Derived typeclass wrapper: Derived[Diff[Person]]. Thanks to that trick, later you will be able to put your modified instance of the Diff typeclass into the implicit scope. The whole process looks as follows:

implicit modifiedDiff: Diff[Person] = Derived[Diff[Person]].ignore(_.name)

Tagging support

Support for tagged types can be added easily by providing an additional generic instance of the Diff type class

implicit def taggedDiff[T:Diff, U]: Diff[T @@ U] = Diff[T].contramap(identity)