[英]How emulate a templatised std::function in C++
Following is a basic instance of what I am doing in my C++
program. 以下是我在C++
程序中所做的基本实例。 I have a list of listeners which are all std::function
s. 我有一个监听器列表,它们都是std::function
s。 I have a concept DataType
which means what kind of data the listener is interested in. The idea here is the same as publish-subscribe pattern. 我有一个概念DataType
,它意味着听众感兴趣的是什么类型的数据。这里的想法与发布 - 订阅模式相同。 A method interested in certain kind of data should be able to add itself to the list of listeners using AddListener
. 对某种数据感兴趣的方法应该能够使用AddListener
将自己添加到侦听器列表中。 Some methods are added & they receive a callback whenever required. 添加了一些方法,并在需要时接收回调。
The program works fine !! 该程序工作正常!!
#include <iostream>
#include <functional>
#include <vector>
#include <string>
enum class DataType {
Type_1,
Type_2
// and so on
};
typedef std::function<void(std::pair<DataType, std::string>)> MyListenerType;
//template <typename T>
//typedef std::function<void(T>)> MyListenerType;
// How can I emulate the above so that a method passing any kind of primitive data-type namely "int, bool, float or double" can be added into
// my vector of listners.
std::vector<MyListenerType> my_data_listeners_1;
std::vector<MyListenerType> my_data_listeners_2;
void ListenerMethod_Instance_1(std::pair<DataType, std::string> information) {
DataType data_type = information.first;
std::string message = information.second;
std::cout << "ListenerMethod_Instance_1 called with message " << message << "\n";
}
void ListenerMethod_Instance_2(std::pair<DataType, std::string> information) {
DataType data_type = information.first;
std::string message = information.second;
std::cout << "ListenerMethod_Instance_2 called with message " << message << "\n";
}
void AddListener (MyListenerType listener, DataType type_of_interest) {
if (DataType::Type_1 == type_of_interest) {
my_data_listeners_1.push_back(listener);
std::cout << "Added a method instance for DataType::Type_1" << "\n";
}
else if (DataType::Type_2 == type_of_interest) {
my_data_listeners_2.push_back(listener);
std::cout << "Added a method instance for DataType::Type_2" << "\n";
}
else {
std::cout << "Listener type not supported" << "\n";
}
}
void CallAllListnersWhohaveSuscribed() {
if (!my_data_listeners_1.empty()) {
std::string send_message_1 = "some message 123";
std::pair <DataType, std::string> info_to_send_1 = std::make_pair (DataType::Type_1, send_message_1);
for(auto const &listener : my_data_listeners_1) {
listener(info_to_send_1);
}
}
if (!my_data_listeners_2.empty()) {
std::string send_message_2 = "some message 456";
std::pair <DataType, std::string> info_to_send_2 = std::make_pair (DataType::Type_2, send_message_2);
for(auto const &listener : my_data_listeners_2) {
listener(info_to_send_2);
}
}
}
int main() {
// Add ListenerMethod_Instance_1 for instance
DataType data_type_1 = DataType::Type_1;
auto listener_instance_1 = std::bind(ListenerMethod_Instance_1, std::placeholders::_1);
AddListener(listener_instance_1, data_type_1);
// Add ListenerMethod_Instance_2 for instance
DataType data_type_2 = DataType::Type_2;
auto listener_instance_2 = std::bind(ListenerMethod_Instance_2, std::placeholders::_1);
AddListener(listener_instance_2, data_type_2);
CallAllListnersWhohaveSuscribed();
return 0;
}
Following is the output of the program: 以下是该计划的输出:
./stdFunctionTest
Added a method instance for DataType::Type_1
Added a method instance for DataType::Type_2
ListenerMethod_Instance_1 called with message some message 123
ListenerMethod_Instance_2 called with message some message 456
But here is how I want to modify & struggling with. 但这就是我想要修改和挣扎的方式。 The caveat is that every ListenerMethod_Instance_1
& ListenerMethod_Instance_2
have to parse the pair to get their info which I don't want to. 需要注意的是,每个ListenerMethod_Instance_1
和ListenerMethod_Instance_2
都必须解析该对以获取我不想要的信息。 I want to enable a method of any C++ primitive data type be it "int, bool, float or double" to be able to be added into the listeners vector & receive the callback . 我想启用任何C ++原始数据类型的方法,无论是“int,bool,float还是double”,都可以添加到侦听器向量中并接收回调 。 For example following method should be "add-able" into AddListener
. 例如,以下方法应该“添加”到AddListener
。
void ListenerMethod_Instance_3(int integer_data) {
std::cout << "ListenerMethod_Instance_3 called with integer_data " << integer_data << "\n";
}
Looking at this link here looks somewhat possible someway. 看这个链接在某种程度上看起来有点可能。 But I'm struggling to adapt it to my use-case here. 但是我在努力使它适应我的用例。 Please suggest. 请建议。
So, basically how can I achieve templates functionality with std::function
s ? 那么,基本上我如何用std::function
s实现模板功能呢?
struct anything_view_t {
void* ptr=0;
template<class T, std::enable_if_t<!std::is_same<anything_view_t, std::decay_t<T>>{}, int> =0>
anything_view_t(T&&t):ptr(std::addressof(t)){}
anything_view_t()=default;
anything_view_t(anything_view_t const&)=default;
anything_view_t& operator=(anything_view_t const&)=default;
template<class T>
operator T() const { return *static_cast<T*>(ptr); }
};
this is a very unsafe type erasing view of anything. 这是一种非常不安全的类型擦除视图。
struct any_callbacks {
std::unordered_map<std::type_index, std::vector<std::function<void(anything_view_t)>>> table;
template<class T>
void add_callback( std::function<void(T)> f ){
table[typeid(T)].push_back(f);
}
template<class T>
void invoke_callbacks(T t) const {
auto it = table.find(typeid(T));
if (it==table.end()) return;
for(auto&&f:it->second)
f(t);
}
};
something like the above should work. 像上面这样的东西应该工作。 The type T
must match exactly. 类型T
必须完全匹配。 References not supported. 参考不受支持。 Code not compiled, design is sound, probably has typos. 代码未编译,设计合理,可能有拼写错误。
This is not restructed to primitive types. 这不会被重构为原始类型。 You should pass T
explicitly, don't rely on deduction as that is fragile. 你应该明确地传递T
,不要依赖扣除,因为它是脆弱的。
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