The forEach function was discussed in the chapter about functions. It is an alternative to a for loop, so it performs an action on each element of the list:
listOf("A", "B", "C").forEach { print(it) } // prints: ABC
Since Kotlin 1.1, there is a similar function, onEach, that also invokes an action on each element. It returns an extension receiver so we can invoke an action on each element in the middle of stream processing. This is commonly used for logging purposes. Here is an example:
(1..10).filter { it % 3 == 0 }
.onEach(::print) // Prints: 369
.map { it / 3 }
.forEach(::print) // Prints: 123
