C++Talk.NET

Daniel Krügler · Guest

After reading about the current application of std::tr1::tuple_size in

http://www2.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf

I found that it should should result in well-formed code if one of the for
the following class templates are used as template arguments:

std::pair<typename, typename>
std::tr1::tuple<...>
std::tr1::array<typename, size_t>

I suggest, that

template<size_t N> class bitset

should also provide a similar tuple interface. I propose to add the
following clauses:

"Tuple interface to class template bitset [tr.bitset.tuple]
tuple_size<bitset::value
1 Return type: integral constant expression.
2 Value: N
tuple_element<I, bitset::type
3 Requires:0 <= I < N. The program is ill-formed if I is out of bounds.
4 value: The type bool.
template 5 Requires: 0 <= I < N. The program is ill-formed if I is out of bounds.
6 Returns: A reference to the Ith element of a, where indexing is
zero-based.
template 7 Requires: 0 <= I < N. The program is ill-formed if I is out of bounds.
8 Return type: bool.
9 Returns: The value of the Ith element of a, where indexing is zero-based."

To my opinion std::bitset std::tr1::array<typename, size_t> as the static analogon of
std::vector<bool> compared to std::vector<T != bool>.
Another argument is, that std::bitset<size_t> has no compile-time
accessor for its template argument (The member function size() is a
runtime function).

I understand that their might exist dissenting votes to this proposals.
One major argument, I can think of, is that vector<bool> does not
fulfill the C++ Conatiner requirements, and I have to confess, that this
partially is true for std::bitset, too, concerning the tuple-interface,
namely that all other tuple classes do return **real** references to
the underlying tuple elements, while std::bitset<N> does not.

So a minimum proposal would be that there shall exist a specialization
tuple_size<bitset.

Greetings from Bremen,

Daniel Krügler

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