如何以scala形式顯示HList的類型

Question

如何將HList的類型作爲字符串獲取以便我可以打印它。例如"Int :: Long :: String :: HNil"

val gen = Generic[?] 
val typeString: String = ??? 
println("The type is " + typeString) 

我知道它的字符串心不是非常有用的，通常你想從gen.Repr

Answer 1

使用shapeless.Typeable類型：

scala> import shapeless._ 
import shapeless._ 

scala> case class A(i: Int, s: String) 
defined class A 

scala> val gen = Generic[A] 
gen: shapeless.Generic[A]{type Repr = 
    shapeless.::[Int,shapeless.::[String,shapeless.HNil]]} = 
    anon$macro$14$1@56639061 

scala> println(Typeable[gen.Repr].describe) 
Int :: String :: HNil