I was wondering why the Room of Requirement can predict the future, and whether it needs to be empty in order to change?
I clearly remember that in Harry Potter and the Order of Phoenix, Harry thinks he really needs a whistle, and immediately discovers one on the shelf beside him even though it had not been there moments before. (The room also kept adding beds and even toilets in Deathly Hallows.) So, did the room predict he would need the whistle, or did it create one when he thought of it?
In Harry Potter and the Deathly Hallows, Ginny, Tonks, and Mrs. Weasley were inside and needed to leave it so the trio can change the room into the Room of Hidden Things. But if the room can change and create whistles, why can't it create or summon Ravenclaw's Diadem while someone is inside?
So my thoughts are: Either the room can predict the future and knows that Harry will need the whistle, or it can change when someone is in the room. But in that case, there is no need for anyone to leave to retrieve the diadem.
Does anyone understand what I'm trying to say?
EDIT: This question did not provide the answer I am looking for.