CODEWITHSUNDEEP
scalatype-conversioncomparable
Martin Cooper
Martin Cooper

Reputation: 459

Scala. Checking if a Type is Comparable

I have a simple class which takes a generic type, Eg:

class SomeClass[T: TypeTag](someVal: T) = {
  def value = someVal
  def columnType = typeOf[T]
}

I need to check if [T] is Comparable at runtime (I don't want to require that it's comparable, only check if it is or not). If I have an actual instance of [T] (which i don't), I can do the following which works fine...

def canCompareType[T](value: T): Boolean = {
  val compClass = classOf[Comparable[_]]
  compClass.isAssignableFrom(value.getClass)
}

But I can't work out how to do this with just the type definition and not actually having an instance of [T] available. I've tried the following thinking that it looks and seems reasonable...

def canCompareType[T]: Boolean = {
  val compClass = classOf[Comparable[_]]
  compClass.isAssignableFrom(classOf[T])
}

But gives the compile error...

Error: class type required but T found : compClass.isAssignableFrom(classOf[T])

I found a similar answer here, but it again assumes that I have an instance of [T] available.

Cast objects to comparable type

Any ideas how I can resolve this. I have a feeling that I must be pretty close.

Update I need to be able to check also on value types, so I would want canCompareType[Int] to also return true as 100.compareTo(200) is valid.

Thanks

Upvotes: 2

Views: 573

Answers (1)

Dima
Dima

Reputation: 40508

Something like this perhaps?

def foo[T: TypeTag] = typeOf[T] match {
    case t if t <:< typeOf[Comparable[_]] => "Comparable"
    case _ => "Not Comparable"
}

Upvotes: 3

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