non_typelist.h

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#pragma once
 
#include <cstddef>
 
namespace osc
{
    // inspired by the same ideas behind `Typelist`, but for
    // non-type template parameters
 
    // NonTypelist: definition
 
    template<typename T, T...>
    struct NonTypelist;
 
    template<typename T>
    struct NonTypelist<T> {
    };
 
    template<typename T, T Head, T... Tails>
    struct NonTypelist<T, Head, Tails...> {
        static constexpr T head = Head;
        using tails = NonTypelist<T, Tails...>;
    };
 
    // NonTypelist: size (the number of compile-time-values held within)
 
    template<typename NTList>
    struct NonTypelistSize;
 
    template<typename T, T... Els>
    struct NonTypelistSize<NonTypelist<T, Els...>> {
        static constexpr size_t value = sizeof...(Els);
    };
 
    template<typename NTList>
    inline constexpr size_t NonTypelistSizeV = NonTypelistSize<NTList>::value;
 
    // NonTypelist: indexed access
 
    template<typename NTList, size_t Index>
    struct NonTypeAt;
 
    template<typename T, T Head, T... Tails>
    struct NonTypeAt<NonTypelist<T, Head, Tails...>, 0> {
        static constexpr T value = Head;
    };
 
    template<typename T, T Head, T... Tails, size_t Index>
    struct NonTypeAt<NonTypelist<T, Head, Tails...>, Index> {
        static_assert(Index < sizeof...(Tails)+1, "index out of range");
        static constexpr T value = NonTypeAt<NonTypelist<T, Tails...>, Index-1>::value;
    };
}