callConstructor<T> function Null safety

Implementation

T callConstructor<T>(Object constr, List<Object?>? arguments) {
  if (arguments == null) {
    return JS('Object', 'new #()', constr);
  } else {
    assertInteropArgs(arguments);
  }

  if (JS('bool', '# instanceof Array', arguments)) {
    int argumentCount = JS('int', '#.length', arguments);
    switch (argumentCount) {
      case 0:
        return JS('Object', 'new #()', constr);

      case 1:
        var arg0 = JS('', '#[0]', arguments);
        return JS('Object', 'new #(#)', constr, arg0);

      case 2:
        var arg0 = JS('', '#[0]', arguments);
        var arg1 = JS('', '#[1]', arguments);
        return JS('Object', 'new #(#, #)', constr, arg0, arg1);

      case 3:
        var arg0 = JS('', '#[0]', arguments);
        var arg1 = JS('', '#[1]', arguments);
        var arg2 = JS('', '#[2]', arguments);
        return JS('Object', 'new #(#, #, #)', constr, arg0, arg1, arg2);

      case 4:
        var arg0 = JS('', '#[0]', arguments);
        var arg1 = JS('', '#[1]', arguments);
        var arg2 = JS('', '#[2]', arguments);
        var arg3 = JS('', '#[3]', arguments);
        return JS(
            'Object', 'new #(#, #, #, #)', constr, arg0, arg1, arg2, arg3);
    }
  }

  // The following code solves the problem of invoking a JavaScript
  // constructor with an unknown number arguments.
  // First bind the constructor to the argument list using bind.apply().
  // The first argument to bind() is the binding of 't', so add 'null' to
  // the arguments list passed to apply().
  // After that, use the JavaScript 'new' operator which overrides any binding
  // of 'this' with the new instance.
  var args = <dynamic>[null]..addAll(arguments);
  var factoryFunction = JS('', '#.bind.apply(#, #)', constr, constr, args);
  // Without this line, calling factoryFunction as a constructor throws
  JS('String', 'String(#)', factoryFunction);
  // This could return an UnknownJavaScriptObject, or a native
  // object for which there is an interceptor
  return JS('Object', 'new #()', factoryFunction);

  // TODO(sra): Investigate:
  //
  //     var jsObj = JS('', 'Object.create(#.prototype)', constr);
  //     JS('', '#.apply(#, #)', constr, jsObj,
  //         []..addAll(arguments.map(_convertToJS)));
  //     return _wrapToDart(jsObj);
}