C++函数委托
2024-08-24 17:36:59
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_[] != ptr.func_[]) {
return func_[] < ptr.func_[];
}
if (func_[] != ptr.func_[]) {
return func_[] < ptr.func_[];
}
return obj_ < ptr.obj_;
}
///< 相等函数
bool operator ==(const member_ptr& ptr) const
{
if (func_[] != ptr.func_[]) {
return false;
}
if (func_[] != ptr.func_[]) {
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\tparam:" << n << ", data:";
for (int v : avec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
}
int testa2(int n)
{
std::cout << "testa::testa2\tparam:" << n << ", data:";
for (int v : avec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
} protected:
std::vector<int> avec_{ , , };
}; class testb
{
public:
virtual int testb1(int n)
{
std::cout << "testb::testb1\tparam:" << n << ", data:";
for (int v : bvec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
}
int testb2(int n)
{
std::cout << "testb::testb2\tparam:" << n << ", data:";
for (int v : bvec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
} protected:
std::vector<int> bvec_{ , , };
}; class testc : public testa, public testb
{
public:
int testa1(int n) override
{
std::cout << "testc::testa1\tparam:" << 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\tparam:" << 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\tparam:" << 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\tparam:" << n << ", data:";
for (int v : dvec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
}
int testd1(int n)
{
std::cout << "testd::testd1\tparam:" << n << ", data:";
for (int v : dvec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
} protected:
std::vector<int> dvec_{ , , };
}; class teste
{
public:
virtual int test(int n)
{
std::cout << "teste::test\tparam:" << n << ", data:";
for (int v : evec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
}
int teste1(int n)
{
std::cout << "teste::teste1\tparam:" << n << ", data:";
for (int v : evec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
} protected:
std::vector<int> evec_{ , , };
}; class testf : public virtual testd, public virtual teste
{
public:
virtual int test(int n) override
{
std::cout << "teste::test\tparam:" << 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\tparam:" << 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\tparam:" << n << ", data:";
for (int v : gvec_) {
std::cout << v << ",";
}
std::cout << std::endl;
return n;
} protected:
std::vector<int> gvec_{ , , };
}; ///< 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();
}
{
function_delegate<> delegate(&a, &testa::testa2);
delegate();
} ///< TEST testb
testb b;
{
function_delegate<> delegate(&b, &testb::testb1);
delegate();
}
{
function_delegate<> delegate(&b, &testb::testb2);
delegate();
} ///< TEST testc
testc c;
{
function_delegate<> delegate(&c, &testa::testa1);
delegate();
}
{
function_delegate<> delegate(&c, &testa::testa2);
delegate();
}
{
function_delegate<> delegate(&c, &testb::testb1);
delegate();
}
{
function_delegate<> delegate(&c, &testb::testb2);
delegate();
}
{
function_delegate<> delegate(&c, &testc::testa1);
delegate();
}
{
function_delegate<> delegate(&c, &testc::testa2);
delegate();
}
{
function_delegate<> delegate(&c, &testc::testb1);
delegate();
}
{
function_delegate<> delegate(&c, &testc::testb2);
delegate();
}
{
function_delegate<> delegate(&c, &testc::test);
delegate();
} ///< TEST testd
testd d;
{
function_delegate<> delegate(&d, &testd::testd1);
delegate();
}
{
function_delegate<> delegate(&d, &testd::test);
delegate();
} ///< TEST teste
teste e;
{
function_delegate<> delegate(&e, &teste::teste1);
delegate();
}
{
function_delegate<> delegate(&e, &teste::test);
delegate();
} ///< TEST testf
testf f;
{
function_delegate<> delegate(&f, &testd::testd1);
delegate();
}
{
function_delegate<> delegate(&f, &testd::test);
delegate();
}
{
function_delegate<> delegate(&f, &teste::teste1);
delegate();
}
{
function_delegate<> delegate(&f, &teste::test);
delegate();
}
{
function_delegate<> delegate(&f, &testf::testd1);
delegate();
}
{
function_delegate<> delegate(&f, &testf::teste1);
delegate();
}
{
function_delegate<> delegate(&f, &testf::test);
delegate();
} ///< TEST testg
testg g;
{
function_delegate<> delegate(&g, &testg::test);
delegate();
}
std::cout << "function_delegate_unit_test end" << std::endl;
}
} namespace function_delegate_efficiency_test
{
class testa
{
public:
int test(int n)
{
return n + ;
}
}; class testb
{
public:
virtual int test(int n)
{
return n + ;
}
};
class testc : public testb
{
public:
int test(int n) override
{
return n + ;
}
}; ///< 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 = ; i < count; ++i) {
a.test(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tc++ object call:\t\t" << tm << "(ms)" << std::endl;
}
{
time_stamp ts;
std::function<int(int)> func = std::bind(&testa::test, &a, std::placeholders::_1);
for (int i = ; i < count; ++i) {
func(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tstd::function call:\t\t" << tm << "(ms)" << std::endl;
}
{
time_stamp ts;
function_delegate<> delegate(&a, &testa::test);
for (int i = ; i < count; ++i) {
delegate(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tdelegate call:\t\t\t" << tm << "(ms)" << std::endl;
} testc c;
testb* pb = &c;
{
time_stamp ts;
for (int i = ; i < count; ++i) {
pb->test(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tc++ pointer virtual call:\t" << tm << "(ms)" << std::endl;
}
{
time_stamp ts;
std::function<int(int)> func = std::bind(&testb::test, pb, std::placeholders::_1);
for (int i = ; i < count; ++i) {
func(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tstd::function virtual call:\t" << tm << "(ms)" << std::endl;
}
{
time_stamp ts;
function_delegate<> delegate(pb, &testb::test);
for (int i = ; i < count; ++i) {
delegate(i);
}
double tm = ts.milliseconds();
std::cout << "count:" << count << "\tdelegate virtual call:\t\t" << 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
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