From: David Abrahams (dave_at_[hidden])
Date: 2007-06-12 13:44:11
on Tue Jun 12 2007, "John Maddock" <john-AT-johnmaddock.co.uk> wrote:
> define a typedef of the policy class:
>
> using namespace boost::math::policy;
> typedef policy<
> // Set error handling:
> domain_error<throw_on_error>,
> pole_error<throw_on_error>,
> overflow_error<throw_on_error>,
> evaluation_error<throw_on_error>,
> denorm_error<ignor_error>,
> underflow_error<ignor_error>,
> // calculate to 8 decimal digits internally
> digits10<8>,
> // don't promote double->long double for accuracy
> promote_double<false>,
> // Integer quantiles return the "outside edge":
> // below the real value for lower critical values,
> // above it for upper critical values, so that the
> // area inside contains *at least* the requested coverage:
> discrete_quantile<integer_outside_edge>
> > fast_quantile_policy;
>
> static fast_quantile_policy fast_quantile;
>
> Then we can just use:
>
> quantile(
> poisson(100),
> 0.05,
> fast_quantile);
>
> In our actual code.
>
> Currently this policy interface is vapourware: I have enough of a prototype
> implemented to know that it's possible to achieve this syntax (this is
> revision #3 already !), but there's a lot of hairy meta-programming to
> convert that into something that the library's internals can make use of...
> so I'd like to know what folks think before I invest too much time messing
> about with MPL :-)
>
> The main disadvantage I've noticed at present, is that the mangled names of
> the policy class - and therefore all the special functions etc - are *very*
> long.
Why not make it allowable to use derivation:
struct fast_quantile_policy
: policy<
// Set error handling:
domain_error<throw_on_error>,
pole_error<throw_on_error>,
overflow_error<throw_on_error>,
evaluation_error<throw_on_error>,
denorm_error<ignor_error>,
underflow_error<ignor_error>,
// calculate to 8 decimal digits internally
digits10<8>,
// don't promote double->long double for accuracy
promote_double<false>,
// Integer quantiles return the "outside edge":
// below the real value for lower critical values,
// above it for upper critical values, so that the
// area inside contains *at least* the requested coverage:
discrete_quantile<integer_outside_edge>
>
{};
?
That will keep your type names under control.
> This has an impact on error messages: in particular we currently use
> BOOST_CURRENT_FUNCTION to get a nice formatted name of a function that's
> about to throw, but with function names a couple of pages long I don't think
> that will be possible with this interface any more :-(
>
-- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com