struct IpV4Address

{

  private uint ip;

  alias ip this;

​

  string toString()

  {

    import std.conv: to;

    return to!string((ip >>> 24) & 0xFF) ~ "." ~

           to!string((ip >>> 16) & 0xFF) ~ "." ~

           to!string((ip >>> 8) & 0xFF) ~ "." ~

           to!string(ip & 0xFF);

  }

}

void main()

{

  import std.format: format;

  IpV4Address x;

  x = 0x01020304;  // 1.2.3.4

  assert( x ==  0x01020304 );

  assert( format("%s", x) == "1.2.3.4" );

  assert( format("%x", x) == "01020304" );  //format.d(4065): Expected '%s' format specifier for type 'IpV4Address'

}