Modern Native C++ Development for Maximum Productivity

The Discussion

• 

  The type of prime *is* typeable. It is of type: std::function< bool(int) >

• 

  @Ferruccio
  
  That's actually not quite right. A Lambda of the form [](int x) { return true; } is _assignable_ to std::function<bool(int)>, but that's not quite the same as saying the type of the lambda _is_ std::function<bool(int)>.
  
  Consider:
  bool function(int);
  
  struct functor
  {
  bool operator()(int);
  };
  
  //...
  std::function<bool(int)> f;
  
  // I can assign a function pointer to f, is f of type bool (*)(int)?
  f = &function;
  
  // I can assign a functor to f, is f of type functor?
  f = functor();
  
  // And now a lambda
  f = [](int x){ return false; };
  
  In the above example, f is none of a function pointer, a function object, or a lambda, yet it accepts all of them just fine.
  
  Lastly, consider:
  
  decltype([](int x) { return false; }) x = [](int x){ return false; };
  
  In the above, I am trying really really hard to get the correct type of the lambda so I can name the type explicitly, yet (in VS2010 anyway) that won't compile. So, it seems that indeed, the type of a lambda is untypable, even though that doesn't stop us from assigning it to std::function or doing other useful things with it.