Can you list and briefly describe the main types of Subject in RxSwift?

In RxSwift, there are several main types of Subject that combine the properties of Observable and Observer:

1. PublishSubject — does not store previous values. Subscribers only receive events that occur after subscription.

2. BehaviorSubject — stores the last value and immediately sends it to new subscribers.

3. ReplaySubject — stores a specified number of the most recent values and sends them to new subscribers.

4. AsyncSubject — only sends the last value to subscribers, and only after the sequence completes.

Example of using BehaviorSubject:

let subject = BehaviorSubject(value: "Initial")

subject.onNext("Second")

subject.subscribe(onNext: { value in
    print("Received: \(value)")
})

// Will output:
// Received: Second

Each type of Subject is suitable for different scenarios in reactive programming.