code: public String getOperatorFunctionModifier(Expression expr) {
      VariableElement var = TreeUtil.getVariableElement(expr);
      if (var == null) {
        assert TreeUtil.trimParentheses(expr) instanceof ArrayAccess
            : "Expression cannot be resolved to a variable or array access.";
        return "Array";
      }
      String modifier = "";
      if (ElementUtil.isVolatile(var)) {
        modifier += "Volatile";
      }
      if (!ElementUtil.isWeakReference(var) && (var.getKind().isField() || options.useARC())) {
        modifier += "Strong";
      }
      return modifier;
    }
docs: Returns the modifier for an assignment expression being converted to a
  function. The result will be "Array" if the lhs is an array access,
  "Strong" if the lhs is a field with a strong reference, and an empty string
  for local variables and weak fields.