meta.hpp

// Copyright Take Vos 2019.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include <type_traits>
 
namespace tt {
 
template<typename T, typename Head, typename... Tail>
constexpr size_t count_type_if(size_t count = 0) {
    if constexpr (sizeof...(Tail) > 0) {
        return count_type_if<T, Tail...>(std::is_same_v<T, Head> ? count + 1 : count);
    } else {
        return std::is_same_v<T, Head> ? count + 1 : count;
    }
}
 
template<typename T, typename Head, typename... Tail>
constexpr size_t index_of_type(size_t index = 0) {
    static_assert(std::is_same_v<T, Head> || sizeof...(Tail) > 0, "Could not find type");
    if constexpr (sizeof...(Tail) > 0) {
        return (std::is_same_v<T, Head>) ? index : index_of_type<T, Tail...>(index + 1);
    } else {
        return index;
    }
}
 
}