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

on Sat Feb 02 2008, Hansi <> 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 <> 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.

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

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

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