Using a parametered/templated comparison object for priority_queue

[Gaminic]

Hey guys,

Sorry for the long title; it's not as longwinded as you may think.

On several occasions in my project, I need to sort elements (indeces) based on their linked values. Those values are stored in an array. This means the comparison looks like this:
bool operator()(int i, int j) { return someArray[i] > someArray[j]; }

Because this form returns often but someArray may differ, I wrapped this in a template class:

template<class T>
struct sorter {
	std::vector<T>& data;
	sorter(std::vector<T>& __d) : data(__d) {}
	bool operator()(int i, int j) const { return data[i] > data[j]; }
};

(Conceptually, only sorting by '>' makes sense, so ambiguous name is not such a problem.)

Now, I want to use this in a different way: I want to select the K indeces with the lowest value from someArray attached to it. My idea was to build a priority_queue, push the first K elements and then compare all the next elements to PQ.top(), as such:

	INDEX t(0);
	for (; t < someLimit; ++t) {
		pq.push(t);
		if (pq.size() == K) break;
	}    
	for (; t < someLimit; ++t) {
		if (someArray[t] < someArray[pq.top()]) { pq.pop(); pq.push(t); }
	}

My problem, however, is the definition / initialization of the priority_queue object. My first idea was simply std::priority_queue<INDEX> pq(sorter<VALUE>(someArray));, but calling any function on pq provides the error "expression must have class type" (?) when hovering over pq.

My second guess, std::priority_queue<INDEX, std::vector<INDEX>, sorter<VALUE>(someArray)> pq;, provides the error 'expected a ')'' when hovering over someArray.

What is the correct way to initialize this data structure?

[Gaminic]

Think I've found it due to a relevant StackOverflow topic¹:

std::priority_queue<INDEX, std::vector<INDEX>, sorter<VALUE>> pq(someArray);

Very odd syntax in my eyes; the parameters for the comparison object are fed to the constructor of the priority_queue object itself! If someone can explain the logic of this to me, I'd be very happy. I'll be marking this as solved either way.

[1] http://stackoverflow.com/questions/9201113/priority-queue-using-an-object-to-compare-instead-of-a-class