MetaArity.hpp

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#ifndef ARITY_HPP_
#define ARITY_HPP_
 
#include <cstddef>
#include <optional>
 
namespace capy::meta
{
 
enum class MetaArity
{
    N1,
    N2,
    N3,
    N4,
    N5,
    N6,
    N7,
    N8,
    N9,
    N10,
    N11,
    N12,
    N13,
    N14,
    N15,
    N16,
 
    LINEAR_ARITIES_COUNT,
};
 
constexpr std::size_t MAX_LINEAR_META_ARITY = static_cast<std::size_t>(
    MetaArity::LINEAR_ARITIES_COUNT
);
 
consteval std::optional<MetaArity>
    meta_arity_from_args_count(const std::size_t args_count)
{
    if (args_count < 1 || args_count > MAX_LINEAR_META_ARITY) {
        return std::nullopt;
    }
 
    return static_cast<MetaArity>(args_count - 1);
}
 
template<std::size_t ARGS_COUNT>
    requires (meta_arity_from_args_count(ARGS_COUNT).has_value())
constexpr MetaArity meta_arity_from_args_count_v
    = meta_arity_from_args_count(ARGS_COUNT).value();
 
template<typename... Args>
constexpr MetaArity meta_arity_from_args_v = meta_arity_from_args_count_v<sizeof...(Args)>;
    
}
 
#endif // !ARITY_HPP_