# [hana] create aribtrary tuples of integral_constants

2 messages
Open this post in threaded view
|
Report Content as Inappropriate

## [hana] create aribtrary tuples of integral_constants

 Making use of Scott Schurr's str_const (https://github.com/boostcon/cppnow_presentations_2012/blob/master/wed/schurr_cpp11_tools_for_class_authors.pdf?raw=true) I have a constexpr string.class StrConst{public:    template    constexpr StrConst(const char (&str)[N])        : str_(str)        , len_(N - 1)    {        static_assert(N > 1, "not a string");    }    constexpr operator const char*() const    {        return str_;    }    constexpr size_t size() const    {        return len_;    }    constexpr char operator[] (size_t i) const    {        return i < len_ ? str_[i] : throw std::out_of_range("invalid index");    }private:    const char* const str_;    const size_t      len_;};I have another constexpr function which returns the position of the first caret found in a string, starting from position n:constexpr int caretPos(const StrConst& str, size_t n = 0){    if (n == str.size())        return -1;    if (str[n] == '^')        return n;    return caretPos(str, n+1);}I can use the results of caretPos to create a typedef for a std::tuple of std::integral_constants, where the size of the tuple is the number of carets found in the string, and each tuple element is an integral constant whose value is the position of the caret in the string.Here I manually construct this tuple:int main(){    constexpr StrConst s("hello^world^");    constexpr int pos1 = caretPos(s);    constexpr int pos2 = caretPos(s, pos1+1);    using P1 = std::integral_constant;    using P2 = std::integral_constant;    using PosTuple = std::tuple;    static_assert(std::tuple_element_t<0, PosTuple>::value == 5, "");    static_assert(std::tuple_element_t<1, PosTuple>::value == 11, "");}Question:I would now like to generalise this for any input string with any number of carets.templateusing PosTuple = std::tuple...>;How can I generate the sequence of Ns... required here using caretPos or some other means? _______________________________________________ Boost-users mailing list [hidden email] https://lists.boost.org/mailman/listinfo.cgi/boost-users