What is a Composable function and what are its key characteristics?

A Composable function is a regular Kotlin function annotated with @Composable that describes a piece of UI. When called, it emits UI elements into the composition.
Key Characteristics:

• Annotated with @Composable: Must have the annotation to be part of the composition
• Fast and idempotent: Should be fast to execute and produce the same result for the same inputs
• Side-effect free: Should not have side effects in the main body
• Can call other Composables: Can compose other UI elements
• Reactive to state changes: Automatically recomposes when state changes

@Composable
fun UserProfile(user: User) {
    Column {
        Text(text = user.name)
        Text(text = user.email)
    }
}