After playing with Go (golang), I think the biggest flaw in its
syntax is using the period (.) for the package qualifier, which
is not distinct from field selectors and method calls. It's
not horrible and not worth changing, but I still consider it a
minor flaw. Here's an illustrative example:

package main

import "os"

type a struct {
        Args int
}

func main() {
 println(os.Args) // os is a package
        os := a{4}
        println(os.Args) // os is a variable
}

Java has the same issue, but since packages qualifiers in Java
tend to be things like java.util.something or org.apache.something,
they aren't likely to collide with identifiers, and, in practice,
the result is there are compile errors about unknown packages when
using undeclared variables. In Go, package qualifiers are much
more likely to collide with useful names.

If one could go back in time to change it, some alternatives could
be ::, \, or #. Other possibilities include ~, !, @, $, or ?.