Binary search extension for CollectionType in Swift

BinarySearch.swift

extension CollectionType where Index: RandomAccessIndexType {

	/// Finds such index N that predicate is true for all elements up to
	/// but not including the index N, and is false for all elements
	/// starting with index N.
	/// Behavior is undefined if there is no such N.
	func binarySearch(predicate: Generator.Element -> Bool) -> Index {
		var low = startIndex
		var high = endIndex
		while low != high {
			let mid = low.advancedBy(low.distanceTo(high) / 2)
			if predicate(self[mid]) {
				low = mid.advancedBy(1)
			} else {
				high = mid
			}
		}
		return low
	}

}