zio / izumi-reflect

TypeTag without scala-reflect

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@quote: Looks a bit similar to TypeTag

izumi-reflect is a fast, lightweight, portable and efficient alternative for TypeTag from scala-reflect.

izumi-reflect is a lightweight model of Scala type system and provides a simulator of the important parts of the Scala typechecker.

Why izumi-reflect

  1. izumi-reflect compiles faster, runs a lot faster than scala-reflect and is fully immutable and thread-safe,
  2. izumi-reflect supports Scala.js, Scala Native,
  3. izumi-reflect is published for Scala 3, you may check port status here (#22),
  4. izumi-reflect allows you to obtain tags for unapplied type constructors (F[_]) and combine them at runtime.


izumi-reflect has been created by Septimal Mind to power Izumi Project, as a replacement for TypeTag in reaction to a lack of confirmed information about the future of scala-reflect/TypeTag in Scala 3 (Motivation), and donated to ZIO. This repository contains an independent and more conservative copy of the code comparing to Izumi one.



izumi-reflect model of the Scala type system is not 100% precise, but "good enough" for the vast majority of the usecases.

Known limitations are:

  1. Type boundaries support is very limited because of a problematic behavior of Scala 2.13 compiler,
  2. Recursive type bounds (F-bounded types) are not preserved and may produce false positives,
  3. Existential types written with forSome are not supported and may produce unexpected results,
  4. Path-Dependent Types are based on variable names and may cause unexpected results with variables with different names but the same type or vice-versa (vs. Scala typechecker)
  5. At the moment Scala 3 port does not support Path-Dependent Types, and Structural Refinements. This will be fixed in future.


When working on the Scala 3 version of the codebase in Intellij, we recommend importing using BSP mode instead of sbt mode, see Dotty#Importing the Project Using BSP.


build.sbt is generated by sbtgen. During development you may not want to mess with ScalaJS and ScalaNative, you may generate a pure-JVM Scala project:


Once you finished tinkering with the code you may want to generate full project and test it for all the platforms:

./sbtgen.sc --js --native
sbt +test