Nil in Go is typed in theory and sort of untyped in practice(utcc.utoronto.ca)

     var x SomeInterfaceType

     // some number of lines of code

     fmt.Printf("%I\n", x)

  var b *bytes.Buffer       // b is a variable with type *bytes.Buffer
  var r io.Reader           // r is a variable with type io.Reader
  r = b                     // r now holds a value with type *bytes.Buffer and value nil
  b == nil                  // true: b is nil
  r == b                    // true: r and b are equal
  r == (io.Reader)(nil)     // false: r is not a nil io.Reader
  r == (*bytes.Buffer)(nil) // true: r contains a nil *bytes.Buffer
  r == nil                  // false: r is not a nil io.Reader
 

   char *p = 0;        // no cast required
   if (p == 0) ...     // no cast required
   time_t t = time(0); // fine
   char *q = 1;        // error; requires (char *) 1.

   int old_style_string_fun();
   int variadic_fun(char *first, ...);

   old_style_string_fun(0);
   variadic_fun("first", 0);