envflag.go
func Uint64Var(p *uint64, name string, value uint64, usage string) {
	EnvironmentFlags.Uint64Var(p, name, value, usage)
}
func Uint64Var(p *uint64, name string, value uint64, usage string) {
	EnvironmentFlags.Uint64Var(p, name, value, usage)
}
// Uint64Var defines a uint64 flag with specified name, default value,
// and usage string.  The argument p points to a uint64 variable in
// which to store the value of the flag.