c++ - 遍历多种类型

Question

假设我想用 vector<int> 测试一些东西, vector<bool> , vector<string> .我想写这样的东西:

for(type T in {int, bool, string}){
   vector<T> v;
   for(int i = 0; i < 3; ++i){
       v.push_back(randomValue<T>());
   }
   assert(v.size() == 3);
}

我知道该语言中没有这样的功能，但是否可以通过某种方式进行模拟？在某些库中是否有此功能，例如 boost ？

Answer 1

提升.MPL

可以用类型列表来完成——它们在Modern C++ Design: Generic Programming and Design Patterns Applied中有详细讨论。作者:Andrei Alexandrescu

检查 Boost.MPL图书馆。例如 - boost::mpl::for_each

LIVE DEMO

#include <boost/exception/detail/type_info.hpp>
#include <boost/mpl/for_each.hpp>
#include <boost/mpl/vector.hpp>
#include <iostream>
#include <cassert>
#include <vector>
#include <string>

using namespace boost;
using namespace std;

template<typename T>
T randomValue()
{
    return T();
}

struct Benchmark
{
    template<typename T>
    void operator()(T) const
    {
        cout << "Testing " << type_name<T>() << endl;
        vector<T> v;
        for(int i = 0; i < 3; ++i)
        {
           v.push_back(randomValue<T>());
        }
        assert(v.size() == 3);
    }
};

int main()
{
    mpl::for_each<mpl::vector<int, bool, string>>(Benchmark());
}

输出是:

Testing int
Testing bool
Testing std::string

---

C++11 可变参数模板

另一种选择是使用 C++11 可变参数模板:

LIVE DEMO

#include <boost/exception/detail/type_info.hpp>
#include <iostream>
#include <cassert>
#include <vector>
#include <string>

using namespace boost;
using namespace std;

template<typename T>
T randomValue()
{
    return T();
}

struct Benchmark
{
    template<typename T>
    void operator()(T) const
    {
        cout << "Testing " << type_name<T>() << endl;
        vector<T> v;
        for(int i = 0; i < 3; ++i)
        {
           v.push_back(randomValue<T>());
        }
        assert(v.size() == 3);
    }
};

template<typename ...Ts,typename F>
void for_each(F f)
{
    auto &&t = {(f(Ts()),0)...};
    (void)t;
}

int main()
{
    for_each<int, bool, string>(Benchmark());
}