What is the difference among ‘In you come’, ‘Come on in’, and ‘Do come in’?

Question

Bagman suddenly spotted Harry, got up quickly, and bounded forward.

“Ah, here he is! Champion number four! In you come, Harry, in you come … nothing to worry about, it's just the wand weighing ceremony, the rest of the judges will be here in a moment –“ (p303, Harry Potter 4, US edition)

I’d like to know the meaning of 'in you come' by comparing and contrasting it with two other expressions 'come on in' and 'do come in'. These three expressions are vaguely mixed in my mind. I know they are emphasizing 'come in', but are they equal in every way? If there's any difference, when should they be used?

I’d be happy if you could help me.

Answer 1

The main difference is one of formality and/or politeness.

Do come in is the most polite/formal (but not too formal to still be friendly) - the "do" has the sense of please feel free to.

Come on in is slightly less formal. It is often used when there is some sort of hesitation or delay on the part of the listener (e.g. "Come on in, the water's lovely!" - indicating that one brave soul has tested the water, while the others are waiting on the beach; or if someone arrives late and starts apologising on the doorstop "I'm sorry I'm late, we were stuck in traffic, ..." I might say "Don't worry at all! Come on in!")

In you come is the least formal, and comes across as fairly friendly. It is slightly more of a command than the others - I might use it to a small child or an animal, while at the same time lifting or otherwise assisting them to enter.

Answer 2

"In you come" has the connotation that the speaker is physically assisting the addressee to enter the room. In the quote, Bagman bounded forward before speaking, presumably to grab Harry by the hand, arm, or shoulder, guide him in and get him into his spot for the ceremony. I tend to think of it more as a verbalization of an action in progress, rather than as an invitation per se, even if the speaker is merely gesturing for the addressee as he enters, without physically approaching or touching him.

"Do come in" and "Come on in" are both invitations to enter the room, but don't have the connotation of physical assistance involved. "Do come in" sounds more polite, while "Come on in" is more informal.

Answer 3

I'll start off with the easier one:

"Do come in" is a polite way of "urging" the person to come in. It's not authoritative even if there is the "do" being used, but it is definitely compelling, as in that the speaker badly wants the hearer to come in.

"Come on in" has the implication of a command, and an impatient one. It isn't used for politeness, but as a compulsory order. It's basically like "come in!", but with the "on", implies that the hearer has hesitated, and therefore the speaker commands the hearer to proceed or continue comming in.

"In you come" is another friendly way of saying "come in", and is common to hearty and jovial speakers.

To sum up, "do come in " is a polite way of asking at the same time adding an element of obligation, as in urging the hearer to come in. "In you come" is another such politeness speech, but is more compelling than "do come in", because in "do come in", the speaker is begging hearer, but not really telling the hearer to do anything, while in "in you come", it doesn't seem to leave any choice for the hearer, except to come in.

"Come on in" is a command.