An Optimised Version of std::fill

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### An Optimised Version of std::fill

Demonstrates a version of `std::fill` that uses `has_trivial_assign` to determine whether to use `memset` to optimise the fill operation (see fill_example.cpp):

    //
    // fill
    // same as std::fill, but uses memset where appropriate
    //
    namespace detail{

    template <typename I, typename T, bool b>
    void do_fill(I first, I last, const T& val, const boost::integral_constant<bool, b>&)
    {
       while(first != last)
       {
          *first = val;
          ++first;
       }
    }

    template <typename T>
    void do_fill(T* first, T* last, const T& val, const boost::true_type&)
    {
       std::memset(first, val, last-first);
    }

    }

    template <class I, class T>
    inline void fill(I first, I last, const T& val)
    {
       //
       // We can do an optimised fill if T has a trivial assignment
       // operator and if it's size is one:
       //
       typedef boost::integral_constant<bool,
          ::boost::has_trivial_assign<T>::value && (sizeof(T) == 1)> truth_type;
       detail::do_fill(first, last, val, truth_type());
    }