Error(s):

source_file.cpp: In function ‘int main()’:
source_file.cpp:13:7: error: call of overloaded ‘f(main()::<lambda(std::shared_ptr<Message>)>&)’ is ambiguous
   f(f1);
       ^
source_file.cpp:6:6: note: candidate: void f(std::function<void(std::shared_ptr<Message>)>)
 void f(std::function<void(std::shared_ptr<Message>)> arg) {}
      ^
source_file.cpp:7:6: note: candidate: void f(std::function<void(std::unique_ptr<Message>)>)
 void f(std::function<void(std::unique_ptr<Message>)> arg) {}
      ^