[boost] Re: mpl functions, pow_, root_, reciprocal

From: Andy Little (andy_at_[hidden])
Date: 2004-01-31 11:38:52

"David Abrahams" <dave_at_[hidden]> wrote in message
news:uvfmsyz69.fsf_at_boost-consulting.com...
> "Andy Little" <andy_at_[hidden]> writes:
>
> > Hi,
> >     Following preliminary ok of  "pow" mpl metafunction by Alexey
> > Gurtovoy... Here are some basic headers for mpl functions pow_, root_
and
> > reciprocal.
> >
> > useage:
> >     boost::mpl::pow_<type,exponent>::type
> >     boost::mpl::root_<type,exponent>::type
> >     boost::mpl::reciprocal<type>::type
>
> These aren't very interesting metafunctions, since they're all
> equivalent to mpl::always<implementation_defined> ;-)

Oops sorry perhaps read 'undefined',' user defined' not implementation
defined :-)
Not to stay that way just havent had time to write some simple examples.
(pow_<int_,int_> should be easy!) Could use one of my own  but doesnt mean
much to many  -->

The problem is I have specialised plus, minus, multiplies etc. for use in
'expression templates'. (think is right term).
However it would be odd to put these in separate namespace. OTOH I could
derive all from mpl in other namespace, but I didnt want to be 'ad-hoc'. ;-)
But maybe that is how mpl functions should be used?.  Was waiting for the
book ... :-)

    template<
        typename Coherent_exponent ,
        typename Incoherent_mux,
        typename Tag
        typename Exponent
    >
    struct pow_<
                pqs::q_unit<
                    Coherent_exponent,
                    Incoherent_mux,
                    Tag
                >,
                Exponent
    >{ // incoherent and tags removed
        // multiply exponents
        typedef typename pqs::q_unit<
            typename multiplies<
                Coherent_exponent,
                Exponent
            >::type,
            typename Incoherent_mux::zero_type,
            typename Tag::default_type
        >::type type;
    };

>
> What is the reason for the trailing underscores?

In case of pow_  to stop it name-clashing with pow(x,y), if 'using
boost::mpl' ,using std. In case of root_ for similarity with pow.
In case of reciprocal the underscore is very small.  Thought 'power' might
also clash with other names.
But any suggestions appreciated.

regards
Andy Little