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### Optional automatic variables

We could write function `convert` in a slightly different manner, so that it has a single `return`-statement:

    boost::optional<int> convert(const std::string& text)
    {
      boost::optional<int> ans;
      std::stringstream s(text);
      int i;
      if ((s >> i) && s.get() == std::char_traits<char>::eof())
        ans = i;

      return ans;
    }

The default constructor of `optional` creates an unitialized optional object. Unlike with `int`s you cannot have an `optional<int>` in an indeterminate state. Its state is always well defined. Instruction `ans = i` initializes the optional object. It uses the 'mixed' assignment from `int`. In general, for `optional<T>`, when an assignment from `T` is invoked, it can do two things. If the optional object is not initialized (our case here), it initializes the contained value using `T`'s copy constructor. If the optional object is already initialized, it assigns the new value to it using `T`'s copy assignment.