Re: [Boost-users] [parameter] Error using positional arguments

Cromwell Enage writes:

--- David Abrahams wrote:

...

I take it back; I'm pretty sure this has nothing to do with forwarding. On what line of *your code* does that error appear?

The error appears on the line with the // error comment.

The actual error, and not just some line of the instantiation backtrace? That makes no sense to me, because the functions generated by BOOST_PARAMETER_FUN take their arguments by const&. The error should appear wherever you try to bind a non-const reference to the resulting const lvalue. Aha: typedef typename boost::remove_const< ^^^^^^^^^^^^ typename boost::parameter::binding< Params , tag::rng_engine >::type >::type RNGEngine; ... RNGEngine rng_engine = p[example::rng_engine]; According to http://www.boost.org/libs/parameter/doc/html/reference.html#binding, binding::type is always a reference type. Since remove_const is T& when T is const (as it is in this case), you get a reference to const. Thus RNGEngine is boost::mt19937 const& and the error should come here: typedef boost::variate_generator RNG; ... RNG rng(rng_engine, RNGDist(p[min], p[max])); where variate_generator takes its first constructor argument by mutable reference. If my analysis is wrong, please explain how it is so. -- Dave Abrahams Boost Consulting www.boost-consulting.com