Re: [boost] accumulators::histogram

From: David Abrahams (dave_at_[hidden])
Date: 2008-02-02 18:28:13

on Sat Feb 02 2008, Hansi <hansipet-AT-web.de> wrote:

> I have looked now at this but I don't understand how to solve this 
> problem. maybe one can give me some example...then I will finish the 
> histogram.
>
> Best regards
> Hansjörg
>
> David Abrahams schrieb:
>> on Fri Feb 01 2008, Eric Niebler <eric-AT-boost-consulting.com> wrote:
>> 
>>> Hansi Hansi wrote:
>>>> I have looked another time to the implementation of the histogram. If
>>>> we want to implement it in the same class density, than it is needed
>>>> to provide default parameter for density_cache_size or min/max. Is it
>>>> possible to ensure that either density_cache_size or min/max is
>>>> provided as parameter? Sorry for the question but I'm not so familiar
>>>> with parameters...
>>>>
>>> Yes, it's possible. IIRC, a parameter pack is a valid MPL sequence, so 
>>> you can us MPL algorithms to detect the presence or absence of any 
>>> parameter.
>> 
>>   boost::parameter::binding< argpack, tag::parametername, void >::type
>> 
>> will tell you.  If the result is void, the parameter wasn't supplied.

argpack is the type of the argument pack.

    is_same<
        boost::parameter::binding< argpack, tag::parametername, void >::type,
        void
    >::value

is a compile-time constant that is false iff the parameter named
parametername is present in an argument pack of type argpack.

-- 
Dave Abrahams
Boost Consulting
http://boost-consulting.com