[boost] Re: generic uses of optional<T>

From: Eric Friedman (ebf_at_[hidden])
Date: 2003-09-01 01:43:39

Dave Gomboc wrote:
[snip]
> I don't like get() because I cannot write x.get() when x is a POD.  This
> would mean I have to support nilable<T> and T with different code,
> which is exactly what I'm trying to avoid.

Why not overload boost::get again for optional? This would certainly improve
consistency with variant. For instance:

  optional<T> opt;
  ...
  T& r = boost::get<T>(opt); // throws bad_get if opt empty
  T* p = boost::get<T>(&opt); // p is null if opt empty

In the same line, we could make optional visitable:

  class my_visitor : public boost::static_visitor<> {
    void operator()(boost::empty) const
    {
      ...
    }

    void operator()(const T& operand) const
    {
      ...
    }
  };

  boost::apply_visitor( my_visitor(), opt );

Support for visitation would also allow seamless integration with the
typeswitch construct I'm working on:

  switch_(opt)
    = case_<boost::empty>( ... )
    = case_<T>( ... )
    ;

I don't have experience with boost::optional, so I don't know how any of the
above would require changes to its interface or concepts.

My two cents,
Eric