https://github.com/gaeljw/typetrees

This library is intended to solve the use case of getting the erased types of a (generic) parameter. Something which was possible in Scala 2 with TypeTag and is now a bit more complex with Scala 3.
https://github.com/gaeljw/typetrees

classtag generics scala scala3 typetag

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This library is intended to solve the use case of getting the erased types of a (generic) parameter. Something which was possible in Scala 2 with TypeTag and is now a bit more complex with Scala 3.

• Host: GitHub
• URL: https://github.com/gaeljw/typetrees
• Owner: gaeljw
• License: apache-2.0
• Created: 2021-02-10T13:44:33.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2024-10-18T16:27:32.000Z (19 days ago)
• Last Synced: 2024-10-18T16:47:19.806Z (19 days ago)
• Topics: classtag, generics, scala, scala3, typetag
• Language: Scala
• Homepage:
• Size: 91.8 KB
• Stars: 10
• Watchers: 2
• Forks: 1
• Open Issues: 9
• Metadata Files:
  • Readme: README.adoc
  • Changelog: CHANGELOG.md
  • License: LICENSE

Awesome Lists containing this project

README

        
:testdir: src/test/scala/io/github/gaeljw/typetrees

= TypeTrees

:toc:

[link=https://search.maven.org/artifact/io.github.gaeljw/typetrees_3]

image::https://img.shields.io/maven-central/v/io.github.gaeljw/typetrees_3.svg[]

image::https://github.com/gaeljw/typetrees/workflows/Scala%20CI/badge.svg[]

This library is intended to solve the use case of getting the erased types of a (generic) parameter.

Something which was possible in Scala 2 with `+TypeTag+`

and is now a bit more complex with Scala 3.

== Get it

.sbt

[source]

----

libraryDependencies += "io.github.gaeljw" %% "typetrees" % typetreesVersion

----

.Maven

[source,xml]

----

  io.github.gaeljw

  typetrees_${scala.version}

  ${typetrees.version}

----

== Usage

Two implementations are available:

* using implicits (`given` s)

* using macro

|===

|Implementation |Pros 👍 |Cons 👎

|Implicits

|Easier

|Only supports up to 4 generic parameters (i.e. a type `T[A, B, C, D]`)

|Macro

|Can handle all cases

|Requires to be used in `inline` method

|===

=== Using implicits

[source,scala]

----

import io.github.gaeljw.typetrees.TypeTree

import io.github.gaeljw.typetrees.TypeTreeTag

import scala.reflect.ClassTag

val tag: TypeTreeTag = summon[TypeTree[T]].tag // <1>

val classTag: ClassTag[_] = tag.self // <2>

val actualClass: Class[_] = classTag.runtimeClass

val typeParameters: List[TypeTreeTag] = tag.args // <3>

----

<1> Get a `+TypeTreeTag+` for a generic type `+T+`

<2> Get a `+ClassTag+` for this type

<3> Get a `+TypeTreeTag+` for each type parameters if any

==== Examples

The main usage is as follows:

[source,scala]

----

def someGenericMethod[T](t: T)(using typeTree: TypeTree[T]): String = {

    val tag: TypeTreeTag = typeTree.tag

    s"I have been called with a parameter of type $tag"

}

someGenericMethod(Map[String, Int]())

// Gives: I have been called with a parameter of type TypeTreeTag(scala.collection.immutable.Map,List(TypeTreeTag(java.lang.String,List()), TypeTreeTag(Int,List())))

----

Or with context bounds:

[source,scala]

----

def someGenericMethod[T : TypeTree](t: T): String = {

    val tag: TypeTreeTag = summon[TypeTree[T]].tag

    s"I have been called with a parameter of type $tag"

}

----

You can find more examples in our link:{testdir}/TestBehaviorImplicits.scala[tests].

=== Using macro

[source,scala]

----

import io.github.gaeljw.typetrees.TypeTreeTag

import io.github.gaeljw.typetrees.TypeTreeTagMacros.typeTreeTag

import scala.reflect.ClassTag

val tag: TypeTreeTag = typeTreeTag[T] // <1>

val classTag: ClassTag[_] = tag.self // <2>

val actualClass: Class[_] = classTag.runtimeClass

val typeParameters: List[TypeTreeTag] = tag.args // <3>

----

<1> Get a `+TypeTreeTag+` for a generic type `+T+`

<2> Get a `+ClassTag+` for this type

<3> Get a `+TypeTreeTag+` for each type parameters if any

==== Examples

The main usage is as follows, within a generic `+inline+` method:

[source,scala]

----

inline def someGenericMethod[T](t: T): String = {

    val tag: TypeTreeTag = typeTreeTag[T]

    s"I have been called with a parameter of type $tag"

}

someGenericMethod(Map[String, Int]())

// Gives: I have been called with a parameter of type TypeTreeTag(scala.collection.immutable.Map,List(TypeTreeTag(java.lang.String,List()), TypeTreeTag(Int,List())))

----

Or:

[source,scala]

----

inline def someGenericMapMethod[T <: Map[_,_]](map: T): String = {

    val mapTag: TypeTreeTag = typeTreeTag[T]

    val keyTag: TypeTreeTag = mapTag.args(0)

    val valueTag: TypeTreeTag = mapTag.args(1)

    s"I have been called with a Map where key is of type $keyTag and value is of type $valueTag"

}

----

It can also be applied to non generic types: in such case it doesn't need to be part of a `+inline def+` but you probably can just use regular `ClassTag` then.

You can find more examples in our link:{testdir}/TestBehaviorMacro.scala[tests].