How to check whether (type of) a manifest is a subtype of manifest[Numberic[_]]?

Question

First of all, I know that manifests are deprecated and it is better to use TypeTag, but for now, it is not an option for me, so please consider my problem:

How to check whether type represented by a manifest is a subtype of the type represented by manifest[Numberic[_]]?

Actually, I have a function that receives a manifest and I want to check whether it is numeric or not.

def isNumeric(m: Manifest[T]) : Boolean = m <:< manifest[Numeric[_]]

But, it does not work, eg for an input of manifest[Double].

Any idea, how to make it work?

Answer 1

Numeric is a type class and it has nothing with subtyping and Manifest (or TypeTag ).

Double is not a Numeric . T : Numeric in type parameter means there is implicit value of type Numeric[T] in scope. You can't check it via reflection.

Maybe you could search for implicit in macros , but I'm not sure and I don't think it's what you are looking for.

So the answer is: You just can't.

It isn't possible even in theory: there is no information about implicit values in runtime and there is no instance of Manifest[T] in compile time.