如何使用 Scala 反射 API 从单例类型获取底层常量类型 [英] How to get underlying constant type from singleton type with Scala reflection API

问题描述

import scala.reflect.runtime.universe._

val a: 42 = 42
val t: Type = typeOf[a.type]
assert(getConstantType(t).get =:= typeOf[42])

def getConstantType(t: Type): Option[ConstantType] = ???

我通常如何实现 getConstantType 以使上述断言通过?我认为这样的事情是可能的，因为下面的断言通过了:

How could I generally implement getConstantType so that the above assertion passes? I assumed that something like this was possible since the assertion below passes:

assert(t <:< typeOf[42])

t.widen 太过分了，因为它返回 Int.我正在寻找返回 Int(42) 的东西.

t.widen goes too far as it return Int. I'm looking for something that returns Int(42).

推荐答案

尝试

def getConstantType(tp: Type): Option[ConstantType] = {
  def unrefine(t: Type): Type = t.dealias match {
    case RefinedType(List(t), scope) if scope.isEmpty => unrefine(t)
    case t                                            => t
  }

  unrefine(tp) match {
    case SingleType(_, sym) => sym.typeSignature match {
      case NullaryMethodType(t) => unrefine(t) match {
        case c: ConstantType => Some(c)
        case _               => None
      }
      case _                 => None
    }
    case _                   => None
  }
}

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