Re: [Boost-users] [mpl|fusion|tr1]mpl::at_c<std::tr1::tuple<...>, I>::type fails

From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2008-08-25 09:04:36

Markus Werle <numerical.simulation <at> web.de> writes:

> Hi!
> 
> I am using boost_1_36_0 manually patched with the files mentioned in
> http://thread.gmane.org/gmane.comp.lib.boost.user/39093/focus=39106
> 
> I thought that std::tr1::tuple was a valid mpl sequence, but this 
> code here fails. Is this by design?
> 
> ---snip---
> #include <boost/tr1/tuple.hpp>
> #include <boost/mpl/assert.hpp>
> #include <boost/mpl/at.hpp>
> 
> template <typename Tuple, long I>
> struct
> show_problem
> {
> 	typedef typename boost::mpl::at_c<Tuple, I>::type type;
> };
> 
> int main()
> {
>  	typedef std::tr1::tuple<int, int> tuple_t;
> 
>  	typedef boost::mpl::at_c<tuple_t, 1L>::type Ouch;
> }

It's std. So it has to make a difference:

typedef std::tr1::tuple_element< 1L, tuple_t>::type OK;

Looks like we end with a plethora of different compile-time sequences
all using different element access semantics, leaving us with an uncomfortable 
feeling about the TR1 ... where will this end?

Markus