Re: [boost] [GSoC] [Checks] Issue with the design

Subject: Re: [boost] [GSoC] [Checks] Issue with the design
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2011-08-01 18:03:33

On Mon, Aug 1, 2011 at 12:15 PM, Pierre Talbot <
pierre.talbot.6114_at_[hidden]> wrote:
[...]

> I tried to extract the characteristics of a "generic" check and the
> weight is one of these. So I tried to implement the weight policy
> class :
>
> #define _WEIGHT_factory(z,n,unused) \
>  template<BOOST_PP_ENUM_PARAMS(n, int weight)> \
>  struct weight_policy \
>  { typedef typename boost::mpl::vector_c<int BOOST_PP_COMMA_IF(n)
> BOOST_PP_ENUM_PARAMS(n, weight)> weight ; } ; \
>
> BOOST_PP_REPEAT_FROM_TO(1,BOOST_CHECK_LIMIT_WEIGHTS,_WEIGHT_factory,~)
>
> #undef _WEIGHT_factory
>
> But the compiler doesn't like the "struct template parameter
> overloading". Is a limit of the language ? Or am I doing it in the
> wrong way ?
> If it's impossible, I though that we could passed the weights to a
> function that aimed to "build" the vector_c type.
>
[...]

You'll have to generate something like

template< int = invalid_weight, int = invalid_weight, /* repeat some pp
constant # of times, e.g., BOOST_CHECK_LIMIT_WEIGHTS times */, int =
invalid_weight >
struct weight_policy;

template< int weight0 >
struct weight_policy< weight0, invalid_weight, invalid_weight, /* ...and so
on... */, invalid_weight >
{ /* definition */ };

template< int weight0, int weight 1 >
struct weight_policy< weight0, weight1, invalid_weight, /* ...and so on...
*/, invalid_weight >
{ /* definition */ };

You'll need to make use of BOOST_PP_SUB to generate the sequence of
"invalid_weight"s in the specializations.

Also, you may want to have 2 weight policies, weight_policy which takes a
sequence of Boost.MPL integral constants, and weight_policy_c which takes a
sequence of (literal) integral constants (cf. vector and vector_c).

- Jeff