Does a type assertion / type switch have bad performance / is slow in Go?

How slow is using type assertions / type switches in Go, as a method of run-time type discovery?

I’ve heard that in C/C++ for example, discovering types at run time has bad performance. To bypass that, you usually add type members to classes, so you can compare against these instead of casting.

I haven’t found a clear answer for this throughout the www.

Here’s an example of what I’m asking about - Is this considered fast when compared to other type checking methodologies (like mentioned above, or others I’m not aware of)?

func question(anything interface{}) {
    switch v := anything.(type) {
        case string:
        case int32, int64:
        case SomeCustomType: