如何为其他类成员函数编写模板包装器方法？ [英] How to write a template wrapper method for other class member functions?

问题描述

我尝试为具有不同参数的不同功能创建模板包装器。
设置是 A 类，具有两个方法 foo 和栏。另一个类 B 将包装这些方法并添加新功能。

I try to create a templated wrapper for different functions with different parameters. The setup is a class A with the basic implementation of two methods foo and bar. Another class B shall wrap these methods and add new functionality.

以下链接中的解决方案对于非类函数非常适用：
c ++ 11：模板化包装函数

The solution from the following link works very well for non-class functions: c++11: Templated wrapper function

但是如果我尝试从另一个类调用方法，我会得到一个

But if I try to invoke methods from another class I get an error.

#include <algorithm>
#include <functional>
#include <iostream>

class A
{
public:
    void foo(int x) {
        std::cout << "Foo: " << x << std::endl;
    }

    void bar(int x, float y) {
        std::cout << "Bar: " << x << ", " << y << std::endl;
    }
};

class B
{
public:
    void fooAndMore(int x) {
        foobarWrapper(&A::foo, 1);
    }

    void barAndMore(int x, float y) {
        foobarWrapper(&A::bar, 1, 3.5f);
    }

    template<typename  T, typename... Args>
    void foobarWrapper(T&& func, Args&&... args)
    {
        std::cout << "Start!" << std::endl;
        std::forward<T>(func)(std::forward<Args>(args)...);
        std::cout << "End!" << std::endl;
    }
};

int main()
{
    B b;
    b.fooAndMore(1);
    b.barAndMore(2, 3.5f);
}

我希望这样：

Start!
Foo: 1
End!
Start!
Bar: 1, 3.5
End!

但我却得到：

error C2064: term does not evaluate to a function taking 1 arguments
note: see reference to function template instantiation 'void B::foobarWrapper<void(__thiscall A::* )(int),int>(T &&,int &&)' being compiled
    with
    [
        T=void (__thiscall A::* )(int)
    ]

error C2064: term does not evaluate to a function taking 2 arguments
note: see reference to function template instantiation 'void B::foobarWrapper<void(__thiscall A::* )(int,float),int,float>(T &&,int &&,float &&)' being compiled
    with
    [
        T=void (__thiscall A::* )(int,float)
    ]

任何想法如何解决

推荐答案

尝试一下，

#include <algorithm>
#include <functional>
#include <iostream>

class A
{
public:
    void foo(int x) {
        std::cout << "Foo: " << x << std::endl;
    }

    void bar(int x, float y) {
        std::cout << "Bar: " << x << ", " << y << std::endl;
    }
};

class B
{
public:
    void fooAndMore(int x) {
        foobarWrapper(&A::foo, x);
    }

    void barAndMore(int x, float y) {
        foobarWrapper(&A::bar, x, y);
    }

    template<typename  T, typename... Args>
    void foobarWrapper(T func, Args&&... args)
    {
        std::cout << "Start!" << std::endl;

        auto caller = std::mem_fn( func); // Newly added lines
        caller( A(), args...);  // Newly added line

        std::cout << "End!" << std::endl;
    }
};

int main()
{
    B b;
    b.fooAndMore(1);
    b.barAndMore(2, 3.5f);
}

输出：

Start!
Foo: 1
End!
Start!
Bar: 2, 3.5
End!

有关更多详细信息，请参见此链接 std :: mem_fn

See this link for more details std::mem_fn

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