variadic_templates.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
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 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the              *
 * Mozilla Public License Version 2.0                                        *
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 ****************************************************************************/
 
#ifndef VCL_BASE_VARIADIC_TEMPLATES_H
#define VCL_BASE_VARIADIC_TEMPLATES_H
 
#include "base.h"
 
#include <tuple>
#include <typeindex>
 
namespace vcl {
 
template<typename... Args>
struct FirstType
{
    using type = std::tuple_element<0, std::tuple<Args...>>::type;
};
 
template<typename... Args>
using FirstTypeT = typename FirstType<Args...>::type;
 
// https://stackoverflow.com/a/71477756/5851101
template<typename T, typename U, typename... Us>
constexpr uint indexInTypePack()
{
    if constexpr (std::is_same_v<T, U>) {
        return 0;
    }
    else {
        if constexpr (sizeof...(Us)) {
            // there is at least another type to check
            constexpr uint res =
                indexInTypePack<T, Us...>(); // look in the rest of the types
            if constexpr (res == UINT_NULL)  // not found in the rest
                return UINT_NULL;
            else
                return 1 + res; // found
        }
        else { // not found
            return UINT_NULL;
        }
    }
}
 
template<typename U, typename... Us>
uint indexInTypePack(std::type_index ti)
{
    if (ti == typeid(U)) {
        return 0;
    }
    else {
        if constexpr (sizeof...(Us)) {
            // there is at least another type to check
            uint res = indexInTypePack<Us...>(ti);
            if (res == UINT_NULL)
                return UINT_NULL;
            else
                return 1 + res;
        }
        else { // not found
            return UINT_NULL;
        }
    }
}
 
template<typename T, typename... Us>
struct IndexInTypes
{
    static constexpr uint value = indexInTypePack<T, Us...>();
};
 
template<uint I, typename... T>
struct TypeAt
{
    using type = std::tuple_element_t<I, std::tuple<T...>>;
};
 
template<uint I, typename... T>
using TypeAtT = typename TypeAt<I, T...>::type;
 
template<typename... Args>
struct NumberOfTypes
{
    static constexpr uint value = sizeof...(Args);
};
 
template<typename... T>
struct ForEachType
{
    template<typename F>
    static void apply(F&& f)
    {
        (f.template operator()<T>(), ...);
    }
};
 
template<typename T, template<typename...> class Template>
struct IsSpecializationOf : std::false_type
{
};
 
template<template<typename...> class Template, typename... Args>
struct IsSpecializationOf<Template<Args...>, Template> : std::true_type
{
};
 
template<typename T, template<typename...> class Template>
constexpr bool IsSpecializationOfV = IsSpecializationOf<T, Template>::value;
 
template<typename T, template<typename...> class Template>
struct IsDerivedFromSpecializationOf
{
private:
    // Helper to check if T is derived from Template<Args...> for any Args
    template<typename... Args>
    static std::true_type  test(const Template<Args...>*);
    static std::false_type test(...);
 
public:
    static constexpr bool value =
        decltype(test(std::declval<std::remove_cvref_t<T>*>()))::value;
};
 
template<typename T, template<typename...> class Template>
constexpr bool IsDerivedFromSpecializationOfV =
    IsDerivedFromSpecializationOf<T, Template>::value;
 
} // namespace vcl
 
#endif // VCL_BASE_VARIADIC_TEMPLATES_H