Microlibrary for debugging type inference in Scala 3 projects.
Type Logger with Error Lens and Metals in Visual Studio Code.
Type Logger in IntelliJ IDEA.
Excerpt from examples.scala:
def examples: Unit =
import Types.*
import typelogger.*
// Use the `logInferredType` method to log the type that would be inferred for the expression
logInferredType(10 * 4.2) // scala.Double
// You can pass a block of code to it...
logInferredType: // Types.Divergent
val x = 10
val a = A(15)
if x > 5 then a else B("hello")
// ... or use it as an extension method.
List(1, 2, 3).logInferredType // scala.collection.immutable.List[scala.Int]
// If you wnated to see the computed types before the inference you can use the `logComputedType` method instead.
logComputedType: // Types.A | Types.B
val x = 10
val a = A(15)
if x > 5 then a else B("hello")
// You can nest the calls to both functions.
logInferredType: // scala.Char
first(
first(List("abc", "def", "ghi")).logComputedType // java.lang.String
).logComputedType // scala.Char
// Both functions can give you simplified and dealiased form o type
returnDeepAliased(Nil)
.logComputedType // Types.DeepAlias[T] (=:= scala.collection.immutable.List[scala.Option[scala.Nothing]])
.logInferredType // Types.DeepAlias[scala.collection.immutable.Nil] (=:= scala.collection.immutable.List[scala.Option[scala.Nothing]])
// `logComputedType` can also show how the type is widened
val x = new Instance
logComputedType(x) // x <:< Types.Instance
logComputedType(x.inner) // x.inner <:< x.Inner (=:= scala.Int)
end examples-
What is the minimum required Scala version?
Type Logger works with Scala 3.2.0 and newer.
-
Does it have any impact on performance?
It doesn't have any impact on the performance of the compiled code. All the logging is done during the typer phase of the compilation and the methods are not leaving any footprint in later phases and in the compilation output.
Frequent usage of those methods can have a small but non-zero impact on compilation time.