C++函数委托

环境：

　　win7_x64旗舰版、VS2015企业版

场景：

　　C++标准库提供std::function类来将一个对象的调用操作封装在一个对象内部，然后可以委托调用，但是有一些弊端，例如下面的需求：

　　　　我们需要将调用操作封装存储到一个map中，来实现观察者模式或信号槽，由于std::function是在编译期确定类型，导致你无法将不同类型的std::function（例如std::function<void()>和std::function<void(int)>）放入同一个map中。

　　function_delegate里就是为了解决上面的问题而写的。

实现代码：

 function_delegate.h

/**
* @file    function_delegate.h
* @brief   函数委托
* @author  DC
* @date    2019-04-16
* @note
* @example
*          class my_class
*          {
*          public:
*              void test(int a, double b)
*              {
*              }
*          };
*
*          my_class my;
*          function_delegate<> delegate(&my, &my_class::test);
*          delegate(1, 2.0);
*
*/

#ifndef FUNCTION_DELEGATE_H_
#define FUNCTION_DELEGATE_H_

namespace function_delegate_pri
{
    ///< 对象成员函数指针
    class member_ptr
    {
    public:
        ///< 哈希函数
        typedef std::_Bitwise_hash<member_ptr> hash;
        ///< 构造函数
        template<class T, class Func>
        member_ptr(T* obj, Func func)
        {
            obj_ = obj;
            *(Func*)&func_ = func;
        }
        ///< 小于函数
        bool operator <(const member_ptr& ptr) const
        {
            if (func_[0] != ptr.func_[0]) {
                return func_[0] < ptr.func_[0];
            }
            if (func_[1] != ptr.func_[1]) {
                return func_[1] < ptr.func_[1];
            }
            return obj_ < ptr.obj_;
        }
        ///< 相等函数
        bool operator ==(const member_ptr& ptr) const
        {
            if (func_[0] != ptr.func_[0]) {
                return false;
            }
            if (func_[1] != ptr.func_[1]) {
                return false;
            }
            return obj_ == ptr.obj_;
        }
        ///< 调用函数
        template
        <
            typename T,
            typename U,
            typename Result,
            typename ... Args
        >
        Result invoke(Args... args)
        {
            typedef Result(U::*Call)(Args...);
            Call call = *(Call*)&func_;
            return (((T*)obj_)->*call)(args...);
        }

        void* obj_{nullptr};     ///< 对象指针
        ///< 对象成员函数需要使用三个指针，C++多重虚拟继承导致
        void* func_[3]{nullptr}; ///< 类成员函数指针
    };

    ///< 函数委托
    template<class Strategy = void>
    class delegate_impl
    {
    public:
        ///< 设置对象和成员函数
        template
        <
            typename T,
            typename U,
            typename Result,
            typename ... Args
        >
        delegate_impl(T* ptr, Result(U::*fn)(Args...)) : refcnt_(ptr), ptr_(ptr, fn)
        {
            typedef Result(*Invoke)(member_ptr*, Args...);
            Invoke call = &delegate_impl::invoke<T, U, Result, Args...>;
            invoke_ = call;
        }

        bool operator <(const delegate_impl& func) const
        {
            if (invoke_ != func.invoke_) {
                return invoke_ < func.invoke_;
            }
            return ptr_ < func.ptr_;
        }

        ///< 调用成员函数
        template
        <
            typename Result = void,
            typename ... Args
        >
        Result operator()(Args... args) const
        {
            typedef Result(*Invoke)(member_ptr*, Args...);
            Invoke call = (Invoke)invoke_;
            return call((member_ptr*)&ptr_, args...);
        }

        Strategy* object() const { return refcnt_; }

    private:
        template
        <
            typename T,
            typename U,
            typename Result,
            typename ... Args
        >
        static Result invoke(member_ptr* ptr, Args... args)
        {
            return ptr->invoke<T, U, Result>(args...);
        }

        Strategy*       refcnt_{ nullptr };   ///< 
        member_ptr    ptr_;                 ///< 成员函数指针
        void*           invoke_{ nullptr };   ///< invoke函数地址
    };

    template<>
    class delegate_impl<void>
    {
    public:
        ///< 设置对象和成员函数
        template
        <
            typename T,
            typename U,
            typename Result,
            typename ... Args
        >
        delegate_impl(T* ptr, Result(U::*fn)(Args...)) : ptr_(ptr, fn)
        {
            typedef Result(*Invoke)(member_ptr*, Args...);
            Invoke call = &delegate_impl::invoke<T, U, Result, Args...>;
            invoke_ = call;
        }

        bool operator <(const delegate_impl& func) const
        {
            if (invoke_ != func.invoke_) {
                return invoke_ < func.invoke_;
            }
            return ptr_ < func.ptr_;
        }

        ///< 调用成员函数
        template
        <
            typename Result = void,
            typename ... Args
        >
        Result operator()(Args... args) const
        {
            typedef Result(*Invoke)(member_ptr*, Args...);
            Invoke call = (Invoke)invoke_;
            return call((member_ptr*)&ptr_, args...);
        }

    private:
        template
        <
            typename T,
            typename U,
            typename Result,
            typename ... Args
        >
        static Result invoke(member_ptr* ptr, Args... args)
        {
            return ptr->invoke<T, U, Result>(args...);
        }

        member_ptr    ptr_;                 ///< 成员函数指针
        void*         invoke_{ nullptr };   ///< invoke函数地址
    };
}

using function_ptr = function_delegate_pri::member_ptr;
template<class Strategy = void>
using function_delegate = function_delegate_pri::delegate_impl<Strategy>;

#endif ///< !FUNCTION_DELEGATE_H_

测试代码：

function_delegate_test.h

#include <iostream>
#include <vector>
#include <functional>
#include "time_stamp.h"
#include "function_delegate.h"

namespace function_delegate_unit_test 
{
    class testa
    {
    public:
        virtual int testa1(int n)
        {
            std::cout << "testa::testa1	param:" << n << ", data:";
            for (int v : avec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
        int testa2(int n)
        {
            std::cout << "testa::testa2	param:" << n << ", data:";
            for (int v : avec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }

    protected:
        std::vector<int> avec_{ 1, 2, 3 };
    };

    class testb
    {
    public:
        virtual int testb1(int n)
        {
            std::cout << "testb::testb1	param:" << n << ", data:";
            for (int v : bvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
        int testb2(int n)
        {
            std::cout << "testb::testb2	param:" << n << ", data:";
            for (int v : bvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }

    protected:
        std::vector<int> bvec_{ 4, 5, 6 };
    };

    class testc : public testa, public testb
    {
    public:
        int testa1(int n) override
        {
            std::cout << "testc::testa1	param:" << n << ", data:";
            for (int v : bvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return testa::testa1(n);
        }

        int testb1(int n) override
        {
            std::cout << "testc::testb1	param:" << n << ", data:";
            for (int v : bvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return testb::testb1(n);
        }

        int test(int n)
        {
            std::cout << "testc::testb1	param:" << n << ", data:";
            for (int v : avec_) {
                std::cout << v << ",";
            }
            for (int v : bvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
    };

    class testd
    {
    public:
        virtual int test(int n)
        {
            std::cout << "testd::test	param:" << n << ", data:";
            for (int v : dvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
        int testd1(int n)
        {
            std::cout << "testd::testd1	param:" << n << ", data:";
            for (int v : dvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }

    protected:
        std::vector<int> dvec_{ 1, 2, 3 };
    };

    class teste
    {
    public:
        virtual int test(int n)
        {
            std::cout << "teste::test	param:" << n << ", data:";
            for (int v : evec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
        int teste1(int n)
        {
            std::cout << "teste::teste1	param:" << n << ", data:";
            for (int v : evec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }

    protected:
        std::vector<int> evec_{ 1, 2, 3 };
    };

    class testf : public virtual testd, public virtual teste
    {
    public:
        virtual int test(int n) override
        {
            std::cout << "teste::test	param:" << n << ", data:";
            for (int v : dvec_) {
                std::cout << v << ",";
            }
            for (int v : evec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;

            testd::test(n);
            teste::test(n);
            return n;
        }
        int testf1(int n)
        {
            std::cout << "testf::testf1	param:" << n << ", data:";
            for (int v : dvec_) {
                std::cout << v << ",";
            }
            for (int v : evec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }
    };

    class testg
    {
    public:
        int test(int n)
        {
            std::cout << "testg::test	param:" << n << ", data:";
            for (int v : gvec_) {
                std::cout << v << ",";
            }
            std::cout << std::endl;
            return n;
        }

    protected:
        std::vector<int> gvec_{ 1, 2, 3 };
    };

    ///< 单元测试
    void test()
    {
        std::cout << "function_delegate_unit_test start" << std::endl;
        ///< TEST testa
        testa a;
        {
            function_delegate<> delegate(&a, &testa::testa1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&a, &testa::testa2);
            delegate(1000);
        }

        ///< TEST testb
        testb b;
        {
            function_delegate<> delegate(&b, &testb::testb1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&b, &testb::testb2);
            delegate(1000);
        }

        ///< TEST testc
        testc c;
        {
            function_delegate<> delegate(&c, &testa::testa1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testa::testa2);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testb::testb1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testb::testb2);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testc::testa1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testc::testa2);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testc::testb1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testc::testb2);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&c, &testc::test);
            delegate(1000);
        }

        ///< TEST testd
        testd d;
        {
            function_delegate<> delegate(&d, &testd::testd1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&d, &testd::test);
            delegate(1000);
        }

        ///< TEST teste
        teste e;
        {
            function_delegate<> delegate(&e, &teste::teste1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&e, &teste::test);
            delegate(1000);
        }

        ///< TEST testf
        testf f;
        {
            function_delegate<> delegate(&f, &testd::testd1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &testd::test);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &teste::teste1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &teste::test);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &testf::testd1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &testf::teste1);
            delegate(1000);
        }
        {
            function_delegate<> delegate(&f, &testf::test);
            delegate(1000);
        }

        ///< TEST testg
        testg g;
        {
            function_delegate<> delegate(&g, &testg::test);
            delegate(1000);
        }
        std::cout << "function_delegate_unit_test end" << std::endl;
    }
}

namespace function_delegate_efficiency_test
{
    class testa
    {
    public:
        int test(int n)
        {
            return n + 1;
        }
    };

    class testb
    {
    public:
        virtual int test(int n)
        {
            return n + 1;
        }
    };
    class testc : public testb
    {
    public:
        int test(int n) override
        {
            return n + 2;
        }
    };

    ///< 性能测试
    void test(int count)
    {
        std::cout << "function_delegate_efficiency_test start" << std::endl;
        testa a;
        {
            time_stamp ts;
            for (int i = 0; i < count; ++i) {
                a.test(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	c++ object call:		" << tm << "(ms)" << std::endl;
        }
        {
            time_stamp ts;
            std::function<int(int)> func = std::bind(&testa::test, &a, std::placeholders::_1);
            for (int i = 0; i < count; ++i) {
                func(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	std::function call:		" << tm << "(ms)" << std::endl;
        }
        {
            time_stamp ts;
            function_delegate<> delegate(&a, &testa::test);
            for (int i = 0; i < count; ++i) {
                delegate(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	delegate call:			" << tm << "(ms)" << std::endl;
        }

        testc c;
        testb* pb = &c;
        {
            time_stamp ts;
            for (int i = 0; i < count; ++i) {
                pb->test(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	c++ pointer virtual call:	" << tm << "(ms)" << std::endl;
        }
        {
            time_stamp ts;
            std::function<int(int)> func = std::bind(&testb::test, pb, std::placeholders::_1);
            for (int i = 0; i < count; ++i) {
                func(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	std::function virtual call:	" << tm << "(ms)" << std::endl;
        }
        {
            time_stamp ts;
            function_delegate<> delegate(pb, &testb::test);
            for (int i = 0; i < count; ++i) {
                delegate(i);
            }
            double tm = ts.milliseconds();
            std::cout << "count:" << count << "	delegate virtual call:		" << tm << "(ms)" << std::endl;
        }
        std::cout << "function_delegate_efficiency_test end" << std::endl;
    }
}

　　1）其中time_stamp.h包含一个计时类time_stamp的实现，这里没贴代码，可以自己实现。

　　2）function_delegate类使用成员data_[0]、data_[1]和data_[2]存储成员函数指针是为了处理被委托的类存在多重继承的情况（用于动态调整this指针，编译器自动调整），如果只使用一个void*存储会发生崩溃。

　　注意：这里有个奇怪的现象，对于使用虚拟继承类成员函数，在我的台式机上测试只需要使用data_[0]和data_[1]即可，而在我的笔记本上测试需要使用data_[0]、data_[1]和data_[2] ，所以我统一使用data_[3]存储。

扩展：

　　1）function_delegate类可以用于实现观察者模式和信号槽等，后面会有单独的文章说明。

　　2）关于C++ 成员函数指针使用两个void*存储的原因：https://www.oschina.net/translate/wide-pointers?cmp