In Scala 2.10, a new reflection library was introduced to add a more powerful toolkit of general reflective capabilities to Scala. Along with full-featured runtime reflection for Scala types and generics, Scala 2.10 also ships with compile-time reflection capabilities, in the form of macros, as well as the ability to reify Scala expressions into abstract syntax trees.
Questions tagged [scala-reflect]
278 questions
2
votes
0 answers
How to recognize an outer variable which is listed between members by reflection?
I have a function which constructs a map by reflection from an object literal (the purpose is to make porting some JavaScript code easier). The function works fine, but I have found a case in which the reflections lists variables from an enclosing…
Suma
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2
votes
1 answer
Access to annotation value in Scala 3.0
I created annotation in scala and used it as follows:
object Main extends App {
println(classOf[Annotated].getAnnotations.length)
import scala.reflect.runtime.universe._
val mirror = runtimeMirror(cls.getClassLoader)
}
final class…
Nik Kashi
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2
votes
1 answer
In scala 2.13, why sometimes TypeTags cannot be inferred? And how to construct one from a variable symbol?
Here is a simple example in shapeless:
it("from Witness") {
val ttg = implicitly[TypeTag[Witness.Lt[String]]]
val ctg = implicitly[ClassTag[Witness.Lt[String]]]
}
it("... from macro") {
val ttg =…
tribbloid
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2
votes
2 answers
In Scala, is it possible to instantiate an object of generic type T?
In Scala, even if the solution is not elegant, is it possible to instantiate/create a new object of a generic type T? Is it possible to achieve this using reflection?
For example, I am interested in something like the following:
case class…
code
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2
votes
1 answer
How to use quasiquotes with previously defined object
I just started studying scala compile-time reflection, and I got introduced to quasiquotes by the Scala official guides.
One concept I'm still struggling with is how am I supposed to work with quasiquotes (or reify, for that matter) if I want to…
Lucas Lima
- 832
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2
votes
2 answers
How to compare the return type of a method to a Scala native or TypeTag?
So, I'm using the Scala reflections library, and I'm trying to check if a method conforms to a given type. To simplify, I'm trying to check only its output.
What I have now is:
val returnType = methodSymbol.returnType
// returnType:…
Lucas Lima
- 832
- 11
- 23
2
votes
1 answer
Instantiating Scala class/case class via reflection
Description
I'm trying to build a tool capable of converting a Map[String, Any] into a class/case class instance. If the class definition contains default parameters which are not specified in the Map, then the default values would apply.
The…
Diego Hermida
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2
votes
2 answers
How to get generic simple class name from scala TypeTag?
How can I get the simple class name including generic using TypeTag? I think that the method signature should be like:
def getClassName[A: TypeTag](a: A): String
getClassName(Map("a" -> 123)) should return Map[String,Int].
Things I've tried:
def…
krismath
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2
votes
1 answer
In Scala, why it is impossible to infer TypeTag from type alias or dependent type?
I have a simple scala program to test the Capability of Scala to infer type classes:
import scala.reflect.ClassTag
object InferTypeTag {
import org.apache.spark.sql.catalyst.ScalaReflection.universe._
def infer(): Unit = {
type U = (Int,…
tribbloid
- 4,026
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- 64
- 103
2
votes
1 answer
In scala 2 or 3, is it possible to debug implicit resolution process in runtime?
In scala language, implicit resolution is often done in compile-time and sometimes throws obfuscating error information, one famous example of such error is when shapeless Generic throws error information like:
error: could not find implicit value…
tribbloid
- 4,026
- 14
- 64
- 103
2
votes
0 answers
A toArray function that breaks on primitive type, but works fine when written as a PartialFunction?
Playing around with a reflection-base code I've come a cross a situation where I want to convert a sequence into array. The catch is that the only type information available is in the form of a runtime.universe.Type, and the sequence itself is of…
Worakarn Isaratham
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2
votes
1 answer
How to compile and run Scala code programmatically
I have the following code and I would like to compile it on the fly and run it.
object HelloWorld {
def main(args: Array[String]): Unit = {
println("Hello, world!")
}
}
So far I have tried something like below:
import…
Vishal
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- 93
2
votes
1 answer
Call scala method from object dynamically
I have a scala case class and object like below,
case class User(userId: Long, UserName: String, ts: Timestamp)
object User {
def getRdd(rdd: RDD[JsValue], type : String): RDD[User] = {
val rdd1: RDD[User] = rdd.map(doc =>…
Nachiket Kate
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2
votes
0 answers
Inconsistent result when checking type subtype
Sometimes I get inconsistent result when I check if a class extends a trait. I'm using scala 2.12.8.
My project uses ru.Type to dynamically build a chain of operations. The output of an operation must conform to the input of the next one.
Before…
To-om
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- 6
2
votes
3 answers
No TypeTag available for case class Type
I want to generate a method which will convert an Object into a Map[String, _], and later back from Map[String, _] to Object.
I generate the initial object as follows:
case class Name (firstName : String, lastName : String)
case class Documents…
Ignacio Alorre
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