code: func AssertType(v interface{}, t reflect.Type) reflect.Value {
  	rv := reflect.ValueOf(v)
  	tv := rv.Type()
  	if tv != t {
  		ppe("Value '%v' has type '%s' but expected '%s'.", v, tv, t)
  	}
  	return rv
  }
docs: // AssertType panics with a `TypeError` if `v` does not have type `t`.
  // Otherwise, it returns the `reflect.Value` of `v`.