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Add new traits named has_no_bounds.

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It is for special usecase: some thing like a window function.
This commit relative to c9ae4fc886 .
Users who wants to access out-of-bounds of sequence, specify new
category to it.

    struct sequence {
        struct category
            : fusion::random_access_traversal_tag
            , fusion::no_bounds_tag {};
        ...
    };

All of bounds related intrinsics of the /no-bounds-sequence/ *should*
guarantee to be well-defined or SFINAE-friendly, or compile error.
This commit is contained in:
Kohei Takahashi
2015-03-20 00:34:37 +09:00
parent 973f2d3940
commit 1e21a4eb7a
3 changed files with 36 additions and 4 deletions
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23
include/boost/fusion/sequence/intrinsic/value_at.hpp
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@ -9,8 +9,13 @@
#include <boost/fusion/support/config.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/or.hpp>
#include <boost/mpl/less.hpp>
#include <boost/mpl/empty_base.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/support/tag_of.hpp>
#include <boost/fusion/support/category_of.hpp>
namespace boost { namespace fusion
{
@ -50,12 +55,26 @@ namespace boost { namespace fusion
struct value_at_impl<std_pair_tag>;
}
namespace detail
{
template <typename Sequence, typename N, typename Tag>
struct value_at_impl
: mpl::if_<
mpl::or_<
mpl::less<N, typename extension::size_impl<Tag>::template apply<Sequence>::type>
, traits::has_no_bounds<Sequence>
>
, typename extension::value_at_impl<Tag>::template apply<Sequence, N>
, mpl::empty_base
>::type
{};
}
namespace result_of
{
template <typename Sequence, typename N>
struct value_at
: extension::value_at_impl<typename detail::tag_of<Sequence>::type>::
template apply<Sequence, N>
: detail::value_at_impl<Sequence, N, typename detail::tag_of<Sequence>::type>
{};
template <typename Sequence, int N>