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
2 answers
java.lang.NoSuchMethodException: scala.collection.immutable.$colon$colon
I am trying to call a function using a variable as String type dynamically i.e. variable will contain a function name as String. So, I need to call a function using that variable.
So, I am using Scala Reflection. It is working if the function is…
Tarun Khaneja
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2
votes
1 answer
What does scala reflection API Type.dealias do?
I have a simple code,
case class Person(name: String, age:Int)
import scala.reflect.runtime.universe._
val t1 = typeOf[Person]
val t2 = t1.dealias
println(t1 == t2)
It outputs true, so I want to ask what is Type.dealias used for? When should I use…
Tom
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2
votes
1 answer
Compilation error "not found value ..." after macros expansion
I'm a newcomer to scala-macros. I'm writing an automated JSON writer/reader for the InfluxDB client.
The reader looks like:
trait InfluxReader[T] {
def read(js: JsArray): T
}
InfluxFormatter:
object InfluxFormatter {
/**
* Generate…
fsanaulla
- 51
- 1
- 5
2
votes
1 answer
How is 'classOf' expression represented in scala AST
I'm new to the Scala AST concepts.
I need to traverse a Scala code tree that contains an expression such as:
classOf[org.apache.commons.lang3.ArrayUtils]
I need to be able to identify this case when pattern matching on…
Natan
- 1,944
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2
votes
1 answer
Did Trees$Literal (reflection) move in Scala 2.13.0-M3?
I'm getting the following 2.13.0-M3 compiler error: type Trees$Literal is not a member of package scala.reflect.internal
This compiled fine under 2.11 and 2.12. In 2.13.0-M3 I get the error in the title. Did this change? An example full line of code…
Greg
- 10,696
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2
votes
0 answers
Case class reflection in scala
I have two questions. First off, this is my reflection code for instantiating a class constructor via reflection:
case class RowToScalaConverter[T: TypeTag]() {
private val tpe: _root_.scala.reflect.runtime.universe.Type = typeOf[T]
…
jmc
- 51
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- 6
2
votes
1 answer
Accessing a case class annotation
case class FieldName(field: String) extends scala.annotation.StaticAnnotation
@FieldName("foo") trait Foo
import scala.reflect.runtime.universe._
symbolOf[Foo].annotations.head
// ann: Annotation = FieldName("type")
How do I access the annotation…
Reactormonk
- 21,472
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2
votes
1 answer
Is the Symbol a case object?
{ sealed trait Sealed; case object Foo extends Sealed; case class Bar(s: String) extends Sealed; trait Baz extends Sealed }
import scala.reflect.runtime.universe._
val List(bar, baz, foo) = symbolOf[Sealed].asClass.knownDirectSubclasses.toList
I've…
Reactormonk
- 21,472
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- 74
- 123
2
votes
0 answers
How does one use Scala reflection to typecheck code in a package parsed from ToolBox?
The following trivial example (run in Scala 2.11.8):
import scala.tools.reflect.ToolBox
import scala.reflect.runtime.currentMirror
object Main extends App {
val toolbox = currentMirror.mkToolBox()
val tree = toolbox.parse {
"""
…
Brian Kent
- 3,754
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2
votes
1 answer
How to write a Scala macro that evaluates to a Tree similar to "reify"
I want to write a macro that captures a program snippet and makes it available as a Tree at runtime. Basically, I want the functionality of reify but embed it in a different syntax. I want to call apply on a Workload companion object, supply some…
Johannes Luong
- 574
- 5
- 19
2
votes
1 answer
In Scala, What is the difference between universe.TypeTag, TypeRef, and Type?
There are 3 different classes all bounded to a universe: TypeTag, TypeRef, and Type. Why do we need all 3? If I only have a Type, how do I convert it to a TypeTag or TypeRef?
E.g. I have obtain a common super type through a Scala reflection API…
tribbloid
- 4,026
- 14
- 64
- 103
2
votes
1 answer
Getting proper type constructor parameters for a "refined" type
I'm having problems comparing the 'compatibility' between two types using reflection (actually I'm writing a macro). For example, I want to permit Vector[Int] === List[Int]. Now I know the general approach. But the problem is I cannot get the type…
0__
- 66,707
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- 171
- 266
2
votes
1 answer
Finding whether a symbol is visible or shadowed at the point of macro expansion
I have a Symbol and want to check if it's visible at the point of macro expansion or shadowed (e.g. by a local variable), so that splicing the symbol's name in the quasiquote doesn't refer to something else.
Looking at…
Alexey Romanov
- 167,066
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2
votes
1 answer
Get field value of a companion object from TypeTag[T]
I have a quite rare use case where a trait is being implemented by 3rd party (think of a plugin architecture) and I want to get a field of each trait's companion object.
A simple trait implementation looks like this:
trait Plugin {
val ID:…
yarinbenado
- 179
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2
votes
0 answers
How to find parent implicit parameter with scala-reflect?
I have two classes:
class X[A](implicit ord: Ordering[A]) // + other irrelevant parameters
class Y[A: Ordering] extends X[A]
Given a Symbol corresponding to Y's implicit constructor parameter, I want to find the symbol for the parent class implicit…
Alexey Romanov
- 167,066
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- 309
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