@cshenton 's answer is not perfect. The "var u = 1.0<<s" in go spec is illegal is because s is a variable, so 1.0 will be deduced as a flaot64. However, in "x[1

@cshenton 's answer is not perfect. The "var u = 1.0<<s" in go spec is illegal is because s is a variable, so 1.0 will be deduced as a flaot64. However, in "x[1.0 << s]", s is a constant, so 1.0 will be deduced as int.