可变参数模板评估

Question

我想知道是否可以将函数传递给可变模板以具有某种逻辑来启用或禁用特定参数。让我解释得更好。我在 C++11 中有一个带有可变参数模板的实体-组件-系统系统，其中实体是简单的 id，组件是数据 and/or 小逻辑函数，所有逻辑都发生在系统内部。系统获得所需的实体，使用可变参数模板搜索具有特定组件列表的实体（我不使用 ids 来检查组件），例如：

var entities = m_world.get<position, direction, acceleration>();

但我想知道是否可以这样做：

var entities = m_world.get<position, direction, acceleration, Except<rotation, whatever>>();

过滤具有特定组件的实体。

我的 ECS 代码可在此处免费获得：https://github.com/arajar/ecs

谢谢。

Answer 1

这很有可能。存档 Search<Include<int, float>, Exclude<std::string, double>>::search();。您可以编写以下代码：

#include <tuple>
#include <typeinfo>
#include <iostream>

template<typename ...Args>
class Search;

template<>
class Search<std::tuple<>, std::tuple<>> {
public:
    static void search() {
    }
};

template<typename T, typename ...Include, typename ...Exclude>
class Search<std::tuple<T, Include...>, std::tuple<Exclude...>> {
public:
    static void search() {
        std::cout << "include: " << typeid(T).name() << std::endl;
        Search<std::tuple<Include...>, std::tuple<Exclude...>>::search();
    }
};

template<typename T, typename ...Exclude>
class Search<std::tuple<>, std::tuple<T, Exclude...>> {
public:
    static void search() {
        std::cout << "exclude: " << typeid(T).name() << std::endl;
        Search<std::tuple<>, std::tuple<Exclude...>>::search();
    }
};

template<typename ...Args>
using Include = std::tuple<Args...>;

template<typename ...Args>
using Exclude = std::tuple<Args...>;

int main() {
    Search<Include<int, float>, Exclude<std::string, double>>::search();
}

可变参数模板评估

Variadic template evaluation

variadic-templates

c++11