无法从std :: bind推导std :: function的模板参数 [英] Could not deduce template argument for std::function from std::bind

问题描述

我试图找到一种方法来调用许多类成员函数，每个成员函数具有不同的参数，并且在调用之前和之后都会发生某些已知的功能。

I'm trying to find a way to call a number of class member functions, each having differing parameters, with certain known functionality happening before and after the call.

这个包装函数是我尝试过的，但例如，对该函数的最终调用不会编译错误：

This wrapper function is what I've tried, but for example the final call to it doesn't compile with error:

'bool包装器（Work *，std :: function< bool（Args ...）>，Args&& ...）'：
不能推断
的模板参数'std :: function< bool（double，std :: string，Args ...）>’来自
’std :: _ Bind< true，bool，std :: _ Pmf_wrap<布尔（__thiscall Work :: *
）（double，std :: string），bool，Work，double，std :: string>，Work * const>'

'bool Wrapper(Work * ,std::function< bool(Args...)>,Args &&...)' : could not deduce template argument for 'std::function< bool(double,std::string,Args...)>' from 'std::_Bind< true,bool,std::_Pmf_wrap< bool (__thiscall Work::* )(double,std::string),bool,Work,double,std::string>,Work *const >'

class Work
    {
    public:
        void DoWork(int a, double b, string c);

    private:
        void Pre() {};
        void Post() {};
        bool Step1() { return true; }
        bool Step2(int) { return true; }
        bool Step3(double, string) { return true; }
    };

template<typename... Args>
bool Wrapper(Work *work, std::function<bool(Args...)> func, Args&&... args)
    {
    work->Pre();
    bool ret = func(std::forward<Args>(args)...);
    work->Post();
    return ret;
    }

void Work::DoWork(int a, double b, string c)
{
    if (!Wrapper<>(this, std::bind(&Work::Step1, this))) // error
        return;
    if (!Wrapper<int>(this, std::bind(&Work::Step2, this), a)) // error
        return;
    if (!Wrapper<double, string>(this, std::bind(&Work::Step3, this), b, c)) // error
        return;
}

int main()
{
    Work work;
    work.DoWork(1, 2.0, "three");
    return 0;
}

（乍看之下，将功能的前置和后置功能一眼看上去更可取，但这是不希望的，因为上面是实际代码的一个大大简化的示例，并且该步骤具有多个返回位置，并且没有测试。）

(Putting the pre- and post- functionality inside the steps would seem at first glance far preferable but that's undesirable as the above is a grossly simplified example of the actual code, and the steps have multiple places of returns, and no tests.)

显式模板参数将使模板解析成为可能。我在做什么错？

I thought the explicit template arguments would make the template resolution possible. What am I doing wrong?

推荐答案

使用C ++ 11， std :: bind 可以被lambda代替，您可以删除包装器模板：

With C++11, std::bind can be replaced by lambda and you can remove template for wrapper :

class Work
{
    public:
        void DoWork(int a, double b, string c);

    private:
        void Pre() {};
        void Post() {};
        bool Step1() { return true; }
        bool Step2(int) { return true; }
        bool Step3(double, string) { return true; }

        friend bool Wrapper(Work *work, std::function<bool()> func);
};

bool Wrapper(Work *work, std::function<bool()> func)
{
    work->Pre();
    bool ret = func();
    work->Post();
    return ret;
}

void Work::DoWork(int a, double b, string c)
{
    if (!Wrapper(this, [this]() -> bool { return this->Step1(); }))
        return;
    if (!Wrapper(this, [this, a]() -> bool { return this->Step2(a); }))
        return;
    if (!Wrapper(this, [this, b, c]() -> bool { return this->Step3(b, c); }))
        return;
}

int main()
{
    Work work;
    work.DoWork(1, 2.0, "three");
    return 0;
}

示例： http://coliru.stacked-crooked.com/a/2cd3b3e2a4abfcdc

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