小编Ned*_*ddy的帖子

我想在c ++ 17中使用以下代码:

#include <iostream>
#include <string>
#include <type_traits>
#include <functional>

class Foo;

template<class T>
class Bar {
public:

    std::function<T(Foo&)> m_fn;

    template<class Fn>
    Bar(Fn fn) : m_fn(fn) {};

    T thing(Foo &foo) const {
        return m_fn(foo);
    }
};


template<class Fn>
Bar(Fn) -> Bar<decltype(std::invoke(std::declval<Fn>(),
                                    std::declval<Foo&>()))>;

class Foo {
public:
    Foo() {};

    template<class T>
    std::vector<T> do_thing(const Bar<T> &b) {
        std::vector<T> r;

        r.push_back(b.thing(*this));

        return r;
    }
};


std::string test(Foo &) {
    return "hello";
}

int main() {
    Foo foo = Foo();

    // works
    std::vector<std::string> …