Difference between revisions of "cpp/container/span"

#include <algorithm>
#include <cstddef>
#include <iostream>
#include <span>
 
template<class T, std::size_t N> [[nodiscard]]
constexpr auto slide(std::span<T,N> s, std::size_t offset, std::size_t width) {
    return s.subspan(offset, offset + width <= s.size() ? width : 0U);
}
 
template<class T, std::size_t N, std::size_t M> [[nodiscard]]
constexpr bool starts_with(std::span<T,N> data, std::span<T,M> prefix) {
    return data.size() >= prefix.size() 
        && std::equal(prefix.begin(), prefix.end(), data.begin());
}
 
template<class T, std::size_t N, std::size_t M> [[nodiscard]]
constexpr bool ends_with(std::span<T,N> data, std::span<T,M> suffix) {
    return data.size() >= suffix.size() 
        && std::equal(data.end() - suffix.size(), data.end(), 
                      suffix.end() - suffix.size());
}
 
template<class T, std::size_t N, std::size_t M> [[nodiscard]]
constexpr bool contains(std::span<T,N> span, std::span<T,M> sub) {
    return std::search(span.begin(), span.end(), sub.begin(), sub.end()) != span.end();
//  return std::ranges::search(span, sub).begin() != span.end();
}
 
void print(const auto& seq) {
    for (const auto& elem : seq) std::cout << elem << ' ';
    std::cout << '\n';
}
 
int main()
{
    constexpr int a[] { 0, 1, 2, 3, 4, 5, 6, 7, 8 };
    constexpr int b[] { 8, 7, 6 };
 
    for (std::size_t offset{}; ; ++offset) {
        static constexpr std::size_t width{6};
        auto s = slide(std::span{a}, offset, width);
        if (s.empty())
            break;
        print(s);
    }
 
    static_assert(
        starts_with( std::span{a}, std::span{a, 4} ) and
        starts_with( std::span{a + 1, 4}, std::span{a + 1, 3} ) and
      ! starts_with( std::span{a}, std::span{b} ) and
      ! starts_with( std::span{a, 8}, std::span{a + 1, 3} ) and
        ends_with( std::span{a}, std::span{a + 6, 3} ) and
      ! ends_with( std::span{a}, std::span{a + 6, 2} ) and
        contains( std::span{a}, std::span{a + 1, 4} ) and
      ! contains( std::span{a, 8}, std::span{a, 9} )
    );
}