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I'm trying to write a multiple functions memoizator, which I've talked about here. The main problem is creating a container containing different and heterogenous functions.

I found a working solution, but I don't know if it's safe, if there are limitations, if it's somehow inefficient or if there is a more elegant solution.

This is my solution:

template <typename ReturnType, typename... Args>
function<ReturnType(Args...)> memoize(function<ReturnType(Args...)> func)
{
    return ([=](Args... args) mutable {
        static map<tuple<Args...>, ReturnType> cache;
        tuple<Args...> t(args...);
        auto result = cache.insert(make_pair(t, ReturnType{}));
        if (result.second) {
            // insertion succeeded so the value wasn't cached already
            result.first->second = func(args...);
        }
        return result.first->second;
    });
}

struct MultiMemoizator
{
    map<string, boost::any> multiCache;
    template <typename ReturnType, typename... Args>
    void addFunction(string name, function < ReturnType(Args...)> func) {
        function < ReturnType(Args...)> cachedFunc = memoize(func);
        boost::any anyCachedFunc = cachedFunc;
        auto result = multiCache.insert(pair<string, boost::any>(name,anyCachedFunc));
        if (!result.second)
            cout << "ERROR: key " + name + " was already inserted" << endl;
    }
    template <typename ReturnType, typename... Args>
    ReturnType callFunction(string name, Args... args) {
        auto it = multiCache.find(name);
        if (it == multiCache.end())
            throw KeyNotFound(name);
        boost::any anyCachedFunc = it->second;
        function < ReturnType(Args...)> cachedFunc = boost::any_cast<function<ReturnType(Args...)>> (anyCachedFunc);
        return cachedFunc(args...);
    }
};

And this is a possible main:

int main()
{
    function<int(int)> intFun = [](int i) {return ++i; };
    function<string(string)> stringFun = [](string s) {
        return "Hello "+s;
    };
    MultiMemoizator mem;
    mem.addFunction("intFun",intFun);
    mem.addFunction("stringFun", stringFun);
    try
    {
        cout << mem.callFunction<int, int>("intFun", 1)<<endl;//print 2
        cout << mem.callFunction<string, string>("stringFun", " World!") << endl;//print Hello World!
        cout << mem.callFunction<string, string>("TrumpIsADickHead", " World!") << endl;//KeyNotFound thrown
    }
    catch (boost::bad_any_cast e)
    {
        cout << "Bad function calling: "<<e.what()<<endl;
        return 1;
    }
    catch (KeyNotFound e) 
    {
        cout << e.what()<<endl;
        return 1;
    }
}
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  • \$\begingroup\$ I recommend that you edit to show the necessary #include lines, both in the code for review and in the sample program (it seems you need Boost, but never mentioned that in the description). \$\endgroup\$ – Toby Speight Sep 6 '17 at 9:36

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