span.h

 
#pragma once
 
#if defined(__cpp_lib_span)
#include <span>
namespace ghassanpl
{
    using std::span;
}
#elif __has_include(<gsl/span>)
#include <gsl/span>
namespace ghassanpl
{
    using gsl::span;
}
#elif __has_include(<gsl/gsl-lite.hpp>)
#include <gsl/gsl-lite.hpp>
namespace ghassanpl
{
    using std20::span;
}
#elif defined(GHPL_SPAN_HEADER)
#include GHPL_SPAN_HEADER
#else
#error "No span implementation found"
#endif
 
namespace ghassanpl
{
    namespace xf {
        template <typename T> [[nodiscard]] constexpr auto as_span() noexcept { return [](auto const& val) { return ghassanpl::span{ val }; }; }
    }
 
    template <typename T>
    [[nodiscard]] span<T> consume_n(span<T>& s, size_t n)
    {
        auto result = s.subspan(0, n);
        s = s.subspan(n);
        return result;
    }
 
    template <typename T>
    [[nodiscard]] decltype(auto) consume(span<T>& s)
    {
        if constexpr (std::is_const_v<T>) {
            auto const& ref = s[0];
            s = s.subspan(1);
            return ref;
        }
        else {
            auto val = std::move(s[0]);
            s = s.subspan(1);
            return val;
        }
    }
}