C ++通用回调实现 [英] C++ generic callback implementation

问题描述

我有一个代码，该代码以XML形式从Flash Player中获取消息，将其解析为函数和参数，并为该函数调用已注册的回调.我要替换的代码段已经很好地完成了(几乎)通用的回调机制:代码用于flashSDK(ASInterface.inl).

I have a code that takes messages from flash player in a form of XML parse them into function and arguments and calls a registered callback for that function. The piece of code that I want to replace is something nicely done (almost) generic Callback mechanism: code for the generic callback implementation of flashSDK (ASInterface.inl).

问题在于此代码是为Flash编写的，我想更换Flash并使用其他具有相同接口的服务.有没有这种回调机制的标准实现(std?boost?其他开源的东西?)?

The problem with it is that this code is written for flash and I want to replace the flash and use other service that will have the same interface. Is there any standard implementation of this callback mechanism (std? boost? something else open sourced?)?

此代码实现了通用的回调机制，您可以在映射中注册具有多个参数和类型的函数:

This code implements generic callbacks mechanism that you can register function with number of arguments and types in a map:

void SomethingHappened(int a, int b) {print a + b;}
void SomethingElseHappened(string abcd) {print abcd;}
callbacks["SomethingHappened"] = &SomethingHappened;
callbacks["SomethingElseHappened"] = &SomethingElseHappened;

，然后搜索并使用参数数组调用:

and than search for it and call with an array of arguments:

Callbacks::iterator itCallback = callbacks.find(functionName);
if (itCallback != callbacks.end())
{
    HRESULT result = itCallback->second.Call(arguments, returnValue);
}

完整用法示例:

//init callbacks
std::map<std::wstring, Callback> callbacks;
void SomethingHappened(int a, int b) {print a + b;}
void SomethingElseHappened(string abcd) {print abcd;}
callbacks[functionName] = &SomethingHappened;

void MessageArrived(string xmlInput)
{
    string functionName = parseFunctionName(xmlInput);
    Callbacks::iterator itCallback = callbacks.find(functionName);
    if (itCallback != callbacks.end())
    {
        //parse arguments
        std::vector<std::wstring> args;
        _Args::split(xml, args);
        ASValue::Array arguments;
        for (size_t i = 0, s = args.size(); i < s; ++i)
        {
            ASValue arg; arg.FromXML(args[i]);
            arguments.push_back(arg);
        }
        ASValue returnValue;
        //***this is where the magic happens: call the function***
        HRESULT result = itCallback->second.Call(arguments, returnValue);
        return result;
    }
}

推荐答案

您可能需要围绕 std :: function 的包装，例如:

You probably need a wrapper around std::function, something like:

template <typename T> struct Tag{};

// Convert ASValue to expected type,
// Possibly throw for invalid arguments.
bool Convert(Tag<Bool>, AsValue val) { return (Boolean)val; }
int Convert(Tag<int>, AsValue val) { return (Number)val; }
// ...

struct Callback
{
private:
    template <std::size_t ... Is, typename Ret, typename ... Ts>
    static Ret call_impl(Ret(* func)(Ts...), std::index_sequence<Is...>)
    {
        if (arr.size() != sizeof...(Is)) throw std::invalid_argument{};
        return func(Convert(tag<Ts>{}, arr[Is])...);
    }
public:
    template <typename Ret, typename ... Ts>
    Callback(Ret(* func)(Ts...)) : Call{[func](ASValue::Array arr, ASValue& ret)
        {
            try
            {
                ret = Callback::call_impl(func, std::make_index_sequence<sizeof(...(Ts)>());
                return S_OK;
            } catch (...) {
                return E_INVALIDARG;
            }
        }}
    {}

    std::function<HRESULT(ASValue::Array, ASValue&)> Call;
};

std :: index_sequence 是C ++ 14，但是您可能会在SO上找到实现.

std::index_sequence is C++14, but you might find implementation on SO.

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