Is “you’re the door on the right.” grammatically correct?

The you is Harry Potter. I’m really curious about the grammatical construction and the reason why JKR chose it.

”Mrs. Weasley, why – ?”

”Ron and Hermione will explain everything, dear, I’ve really got to dash,” Mrs. Weasley whispered distractedly. “There” – they had reached the second landing – “you’re the door on the right. I’ll call you when it’s over.” (Harry Potter 5 [US Version]: p.62)

N.B.: Mrs. Weasley has just led Harry to his room. She is in a rush because she has to attend a meeting downstairs.

I think it means "your room is at the door on the right," but Mrs. Weasley might be making a mistake because she’s in hurry. I don’t know for sure, though.

1. What’s the true meaning of “you’re the door on the right”?
2. If it’s grammatically acceptable, is there any omission in the sentence?
3. If it’s grammatically acceptable, what situation do you use it in? And what’s the difference in listeners’ impressions between this kind (a-person-is-an-object type) of sentence and the more common version?
4. Would you give me some examples of a-person-is-an-object sentences?

Solution 1:

1. Your understanding of the sentence is correct—it means that Harry's room is the one on the right.

2. It is grammatically acceptable, but a sentence that is grammatically correct is not necessarily meaningful. In this case, however, it is understandable, but your phrasing of the sentence would be the complete form.

3. Personally, I would not use this construction; it's a rather unusual one. Using this sentence might imply familiarity or distraction, depending on the observer.

4. I can think of several, but they are not in the same style as your quote. Most sentence of this type, such as You are my doll, use meanings that have become embedded in the language and are reported on in dictionaries. Sentences like those in your quote are extremely unlikely to be encountered and I would not recommend using them.

Solution 2:

Both of the current answers claim that this is unusual usage. I'm just posting an answer to say that, in my experience, it's not unusual at all.

Solution 3:

This is a common but informal variation on the figure of speech called metonym ("name beyond"), where a piece or an aspect of something is equated with the whole, as in "all hands on deck" or "I drank the whole bottle." In this case, the person is directly and explicitly equated to something that belongs to them.

Here are some typical usages:

• Waitress: "OK, you're the steak dinner, right, and you're the fish?"
• Coach: "You're the Green Team today, Sport!"
• Athlete: "Am I the gold medal?"
• Little Red Riding Hood's father: "OK, remember, Granny is the path on the left, the wolf is the path on the right."

It's basically a species of metaphor.

Solution 4:

The omitted word is something akin to "assigned". It is equivalent to "You are assigned the door on the right" or "You are to use the door on the right". It could just as well be understood as "your door is the door on the right".

It is an unusual construct, but one that it certainly grammatically acceptable in conversation. I wouldn't use it in formal writing.

The only other person-as-object structures I could find are metaphors to indicate the person is like the object.