What is the difference between hot and cold streams?

Hot streams:

• Active regardless of observers.
• Always emit the latest available data to subscribers from the moment of subscription.
• Examples: LiveData, StateFlow, SharedFlow.

Cold streams:

• Active only when there is at least one observer.
• Execute logic upon each new subscription.
• Examples: Flow, Sequence.

StateFlow is a specialized SharedFlow that remembers the last value. SharedFlow can be configured to work like StateFlow with a replay buffer of 1.

Key differences:

Operation	Hot stream	Cold stream
Activity	Always	On subscription
Logic execution	Once	On each subscription
State retention	Yes (LiveData, StateFlow, SharedFlow with replay)	No (by default)
Multi-user	Yes	No (each subscriber gets a separate copy)

Hot streams are used to represent UI state or shared data. Cold streams are for performing operations upon subscription, such as network requests or database queries.

Example of a cold stream:

// This stream will load data only when there is a subscriber
fun loadData(): Flow<Data> = flow {
    // Data loading occurs here
    emit(NetworkApi.getData())
}

Example of a hot stream (StateFlow):

// This stream always has a value and is available for subscription
val uiState: StateFlow<UiState> = MutableStateFlow(LoadingUiState)

fun updateState(newState: UiState) {
    uiState.value = newState
}