Incorrect optional parameter argument removal "?"

[andersforsell]

@pavelgj In block.dart attrAccessorFactory the optional argument operator "?" removal was done incorrectly in #23 since one cannot distinguish "explicitly passed null" from "did not pass an optional argument" parameter. :

attrAccessorFactory(dom.Element element, String name) {
  return ([String value]) {
    if (value != null) {
      if (value == null) { // THIS CODE IS NOW DEAD
        element.removeAttribute(name);
      } else {
        element.setAttribute(name, value);
      }
      return value;
    } else {
      return element.getAttribute(name);
    }
  };
}

In a Google+ thread I saw this suggestion for handling similar problem with a special default value:

class Nothing() { const Nothing(); }
class List {
   List([n = const Nothing()]) { if(identical(n, const Nothing()) { ... } else { ... } }
}

[pavelgj]

@andersforsell Nice catch, thanks. Though it appears it is unused code at the moment...

It's an interesting pattern (Nothing), however I think it wouldn't work in checked mode, or it would require stripping the type annotation from value. Type-safe alternative might be:

class NothingString implements String {...}

[mhevery]

This code has been deleted, closing