making a std::funtion that points to two functions c++

Question

If I have two functions

void foo()
{
    std::cout << 1 << std::endl;
}

void bar()
{
    std::cout << 2 << std::endl;
}

and I have a function pointer

std::function<void()> v;

and I want v() to print

1
2

Answer 1

std::function's definition of target is const T* target() const, which means it can only store one target.

This question has been asked before, the situation you're describing is known as "delegate multicasting" in CLR/.NET in the context of event-handlers.

There are a few possible solutions:

1. The first is to use a lambda or other function to define the multicast manually:

   function<void()> v = []() {
       foo();
       bar();
   };
   v();
   

2. The second is to define your own full std::function-esque which supports a variable number of targets. You could do it with a template array (thus avoiding runtime use of vector)... or just use a vector anyway.

3. A third option is to simply wrap vector anyway (warning: pseudocodeish):

   template<class FuncType>
   class MulticastFunction {
   private:
       vector<std::function<FuncType>> targets;
   public:
       void operator()() {
           for(auto& target : this->targets) {
               target();
           }
       }
       void addTarget(FuncType& target) {
           this->targets->push_back( target );
       }
   }
   

   Usage:

   MulticastFunction<void()> mc;
   mc.addTarget( foo );
   mc.addTarget( bar );
   mc();