Using Scala CLI, you can require the entire toolkit in a single line:
//> using toolkit latestAlternatively, you can require just a specific version of UPickle:
//> using dep com.lihaoyi::upickle:4.1.0In your build.sbt file, you can add the dependency on the Toolkit:
lazyvalexample=project.in(file(".")).settings(scalaVersion:="3.4.2",libraryDependencies+="org.scala-lang"%%"toolkit"%"0.7.0")Alternatively, you can require just a specific version of UPickle:
libraryDependencies+="com.lihaoyi"%%"upickle"%"4.1.0"In your build.sc file, you can add the dependency to the upickle library:
objectexampleextendsScalaModule{defscalaVersion="3.4.2"defivyDeps=Agg(ivy"org.scala-lang::toolkit:0.7.0")}Alternatively, you can require just a specific version of UPickle:
ivy"com.lihaoyi::upickle:4.1.0"Serializing a Map to JSON
uPickle can serialize your Scala objects to JSON, so that you can save them in files or send them over the network.
By default it can serialize primitive types such as Int or String, as well as standard collections such as Map and List.
valmap:Map[String, Int]=Map("Toolkitty"->3,"Scaniel"->5)valjsonString:String=upickle.default.write(map)println(jsonString)// prints: {"Toolkitty":3,"Scaniel":5}Serializing a custom object to JSON
In Scala, you can use a case class to define your own data type. For example, to represent a pet owner with the name of its pets, you can
caseclassPetOwner(name:String,pets:List[String])To be able to write a PetOwner to JSON we need to provide a ReadWriter instance for the case class PetOwner. Luckily, upickle is able to fully automate that:
importupickle.default._implicitvalownerRw:ReadWriter[PetOwner]=macroRW[PetOwner]Some explanations:
- An
implicit valis a value that can be automatically provided as an argument to a method or function call, without having to explicitly pass it. macroRWis a method provided by uPickle that can generate a instances ofReadWriterfor case classes, using the information about its fields.
importupickle.default.*caseclassPetOwner(name:String,pets:List[String])derivesReadWriterThe derives keyword is used to automatically generate given instances. Using the compiler’s knowledge of the fields in PetOwner, it generates a ReadWriter[PetOwner].
This means that you can now write (and read) PetOwner objects to JSON with upickle.default.write(petOwner).
Notice that you do not need to pass the instance of ReadWriter[PetOwner] explicitly to the write method. But it does, nevertheless, get it from the context, as “given” value. You may find more information about contextual abstractions in the Scala 3 Book.
Putting everything together you should get:
importupickle.default._caseclassPetOwner(name:String,pets:List[String])implicitvalownerRw:ReadWriter[PetOwner]=macroRWvalpetOwner=PetOwner("Peter",List("Toolkitty","Scaniel"))valjson:String=write(petOwner)println(json)// prints: {"name":"Peter","pets":["Toolkitty","Scaniel"]}"importupickle.default._caseclassPetOwner(name:String,pets:List[String])derivesReadWritervalpetOwner=PetOwner("Peter",List("Toolkitty","Scaniel"))valjson:String=write(petOwner)println(json)// prints: {"name":"Peter","pets":["Toolkitty","Scaniel"]}"