I want to use std::function<void()> as a typename in initializing a map:

namespace kc
{
    class kcmessage
    {
        private:
            std::string value;
            void warning() {}
            void error()
            {
                exit(1);
            }
            std::map<std::string, std::function<void()>> msgtypes = {
                { "WARNING", warning },
                { "ERROR", error }
            };
            int msgtype;
    };
}

But it's not working: error: could not convert ‘{{"WARNING", ((kc::kcmessage*)this)->kc::kcmessage::warning}, {"ERROR", ((kc::kcmessage*)this)->kc::kcmessage::error}}’ from ‘<brace-enclosed initializer list>’ to ‘std::map<std::__cxx11::basic_string<char>, std::function<void()> >’ (<brace-enclosed initializer list>)

CodePudding user response：

If you want to access a member function ( non static ) you have to bind the method to the instance of the class. For that you can use std::bind but it is much easier to simply use a lambda for that purpose.

#include <functional>
#include <map>
#include <string>
#include <iostream>

namespace kc
{
    class kcmessage
    {
        private:
            std::string value;
            void warning() {std::cout << "Waring called!"<<std::endl;}
            void error()
            {
                std::cout << "Error called" << std::endl;
                //exit(1);
            }
            std::map<std::string, std::function<void()>> msgtypes = {
                { "WARNING", [this](){ warning();} },
                { "ERROR", [this](){ error();} }
            };
            int msgtype;

            public:
            void CallAll()
            {
                for( auto& el: msgtypes)
                   {
                       el.second();
                   }
            }
    };
}

int main()
{
    kc::kcmessage{}.CallAll();
}

Execute it here

You can make your methods also static ones, but in this case you can't any longer access your member data if needed which is typically the case.