What is the purpose of using the 'out' keyword in programming?

The keyword out in programming, for example in Kotlin (often used for Android), is used to denote covariance in generics.

This means that a type parameter with out can only be used for output (return values), not for input (function arguments).

Example:

interface Producer<out T> {
    fun produce(): T
}

Here, Producer<out T> guarantees that T is used only for output, allowing safe use of subtypes.

The purpose of out is to ensure type safety and flexibility when working with generics, enabling covariance where appropriate.