13.2 Position Information Parameter

haxe.PosInfos is a magic type which can be used to generate position information into the output for debugging use. If a function has a final optional argument of this type, i.e. (..., ?pos:haxe.PosInfos), each call to that function which does not assign a value to that argument has its position added as a call argument.

It is sometimes useful to define a custom method that does traces in some case. The following usage is possible in Haxe since when the haxe.PosInfos optional parameter is not set, its default value will always be replaced by the compiler:

class Main {
  static function assert(cond:Bool, ?pos:haxe.PosInfos) {
    if (!cond)
      haxe.Log.trace("Assert in " + pos.className + "::" + pos.methodName, pos);

  static function main() {
    assert(1 == 1); // nothing
    assert(0 == 3); // trace "Assert in Test::main"