An Optimized Version of std::copy

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### An Optimized Version of std::copy

Demonstrates a version of `std::copy` that uses `has_trivial_assign` to determine whether to use `memcpy` to optimise the copy operation (see copy_example.cpp):

    //
    // opt::copy
    // same semantics as std::copy
    // calls memcpy where appropriate.
    //

    namespace detail{

    template<typename I1, typename I2, bool b>
    I2 copy_imp(I1 first, I1 last, I2 out, const boost::integral_constant<bool, b>&)
    {
       while(first != last)
       {
          *out = *first;
          ++out;
          ++first;
       }
       return out;
    }

    template<typename T>
    T* copy_imp(const T* first, const T* last, T* out, const boost::true_type&)
    {
       memmove(out, first, (last-first)*sizeof(T));
       return out+(last-first);
    }

    }

    template<typename I1, typename I2>
    inline I2 copy(I1 first, I1 last, I2 out)
    {
       //
       // We can copy with memcpy if T has a trivial assignment operator,
       // and if the iterator arguments are actually pointers (this last
       // requirement we detect with overload resolution):
       //
       typedef typename std::iterator_traits<I1>::value_type value_type;
       return detail::copy_imp(first, last, out, boost::has_trivial_assign<value_type>());
    }