一种优雅地实现C++ string switch的方法

Bruce

#include <unordered_map>
#include <functional>
#include <string>
#include <cstdio>

template <typename T>
class Switch
{
private:
    T expression;
    std::unordered_map<T, std::function<void()>> map;
    std::function<void()> defaultFunction;

public:
    Switch(const T& v) { this->expression = v; }
    Switch& case_(const T& c, const std::function<void()>& f) {
        map[c] = f;
        return *this;
    }
    Switch& default_(const std::function<void()>& f) {
        this->defaultFunction = f;
        return *this;
    }
    virtual ~Switch() {
        if (map[expression]) {
            map[expression]();
        } else {
            defaultFunction();
        }
    }
};

int main(int argc, char* argv[])
{
    if (argc < 2) {
        return 1;
    }
    std::string v(argv[1]);

    Switch<std::string>(v)
        .case_("hello", [] { std::printf("get hello\n"); })
        .case_("world", [] { std::printf("get world\n"); })
        .default_([] { std::printf("get other string\n"); });

    Switch<int>(argc)
        .default_([=] { std::printf("get %d args\n", argc); });

    return 0;
}