> This is funny to me, because Go is often touted as a language that has "everything you need" in the stdlib.

My usual example of something missing from the standard library is

    func max(a, b int) int {
      if a > b {
        return a
      } else {
        return b
      }
    }

math.Max only operates on two float64s (due to the absence of function overloads; many standard library functions such as this predated generics), so if you want to avoid casting (and/or potential loss of precision if you're working with int64), you need to reinvent the wheel.