What would be the idiomatic/semantic way to define...

# random

[Orhan Tozan]

What would be the idiomatic/semantic way to define a limited size length of a collection? Given a data class ChatConversation, where a chat conversation is always between two users (userId), which type would fit the most? I was thinking about a val userIds: Set<Int> but that doesn't enforce the min 2, max 2. Also thought about a val userIds: Pair<Int, Int>, but the fact that Pair(1, 2) == Pair(2, 1) equals to false makes it a inproper fit given the case here, since a conversation between Bob and Alice should be considered the same as a conversation between Alice and Bob.

EDIT: Possible option:

data class TwoSizedSet<T>(val value: Set<T>) {
    init {
        require(value.size == 2)
    }
}

[cedric]

Why use a collection at all? Seems ill-fitted if you know the size ahead of time.

[Orhan Tozan]

Because it makes querying easier and more semantic I think?

[Orhan Tozan]

When I query my repository where userA = 1 and userB = 2 , it forces me to check on both sides (no difference between a conversation of Bob and Alice, and Alice and Bob)

[cedric]

Trying to understand why prefer a collection over data class TwoSize<T>(val first: T, val second: T)

[Orhan Tozan]

Wouldn't that be the same as a Pair<T> ?

[cedric]

although the equal semantic of the class I just wrote will be similar to Pair so you probably don’t want that

[cedric]

hehe you beat me to it 🙂

[cedric]

If you absolutely want a collection but ordering matters, Set is definitely not the right choice though 🙂

[Orhan Tozan]

Why would ordering matter in this case?

[cedric]

That was your own requirement:

the fact that Pair(1, 2) == Pair(2, 1) equals to false makes it a inproper fit given the case here, since a conversation between Bob and Alice should be considered the same as a conversation between Alice and Bob.

[Orhan Tozan]

I thought ordering does not matter, that's why I thought of a Set

[Orhan Tozan]

Perhaps there is a misunderstanding in my wording there. I'm basically saying that I wanted that Pair(1, 2) == Pair(2, 1) equals to true, which isn't the case. That makes the requirement unordered, instead of ordered. Right?

[Orhan Tozan]

Conversation between Bob and Alice is the same as a conversation between Alice and Bob, which is not what the Pair does.

[cedric]

Never mind

[cedric]

Ignore what I wrote

[cedric]

Deleting it

[Orhan Tozan]

It's a tricky one, isn't it😁.