A question regard function object

[LarryChen]

Here is the code,

class IntSequence
{
public:
	IntSequence(int initialValue) : value(initialValue) {}

	int operator()()
	{
		return value++;
	}

private:
	int value;
};

int main()
{		
 	list<int> coll;

	generate_n(back_inserter(coll), 9, IntSequence(1));
  	return 0;
}

In the call of generate_n, generator function IntSequence(1) with an int argument will call operator() but operator() doesn't have any arguments. I wander why? Also if I define operator() as the follows,

int operator()(int elem)
{
     return value+elem;
}

How can I call generate_n?

[monarch_dodra]

Gen: Generator function that takes no arguments and returns some value to be stored as element value

Because the argument is a generator function. That means calling operator()() should generate a new value every time. Like rand(). It doesn't take an argument.

It could, but that's just not how it's designed.

[kempofighter]

How can I call generate_n?

You can't with that second predicate. You can do it with for_each though by designing a predicate that takes a non-const reference to each thing in the container.

Try something like this.

struct IncrementEach
{
   IncrementEach(int value) : value(2) {}
   void operator()(int& elem)
   {
      elem += value;
   }
   const int value;
};

int values[10] = { 0 };
std::for_each(values, values + 10, IncrementEach(2));
std::ostream_iterator<int> strmiter(std::cout, "\n");
std::copy(values, values + 10, strmiter);
std::cout << std::endl;