Question

Scala的反射API是否提供了一种判断Scala对象是否为函数的方法？到目前为止，我提出的最好的是：

import scala.reflect.runtime.universe._

def isFunction[T : TypeTag](x: T) =
  weakTypeOf[T] <:< weakTypeOf[Function0[_]] ||
  weakTypeOf[T] <:< weakTypeOf[Function1[_,_]] ||
  weakTypeOf[T] <:< weakTypeOf[Function2[_,_,_]] ||
  weakTypeOf[T] <:< weakTypeOf[Function3[_,_,_,_]] ||
  weakTypeOf[T] <:< weakTypeOf[Function4[_,_,_,_,_]] ||
  . . .

必须有更好的方法。

Answer 1

据我所知，公共API不允许您这样做，但始终可以访问内部：

scala> val st = scala.reflect.runtime.universe.asInstanceOf[scala.reflect.runtime.JavaUniverse]
st: scala.reflect.runtime.JavaUniverse = scala.reflect.runtime.JavaUniverse@db03ddc

scala> st.definitions.isFunctionType(st.typeOf[Int])
res0: Boolean = false

scala> st.definitions.isFunctionType(st.typeOf[Int => Int])
res1: Boolean = true

scala> st.definitions.isFunctionType(st.typeOf[Function0[Int]])
res2: Boolean = true

scala> st.definitions.isFunctionType(st.typeOf[Function0[_]])
res3: Boolean = true

Answer 2

10:21 ~/Projects/210x/sandbox (2.10.x)$ scala
Welcome to Scala version 2.10.5-20140407-165700-ec05aeb3d6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_40).

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> definitions.FunctionClass.contains(typeOf[Function1[_, _]].typeSymbol)
res1: Boolean = true

10:22 ~/Projects/211x/sandbox (2.11.x)$ scala
Welcome to Scala version 2.11.1-20140509-211642-d079e769b9 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_40).

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> definitions.FunctionClass.seq.contains(typeOf[Function1[_, _]].typeSymbol)
res0: Boolean = true

如何判断Scala对象是否为函数？

2 个答案: