Kotlin Programming: The Big Nerd Ranch Guide, First Edition

apply

First on our tour of the standard functions is apply. apply can be thought of as a configuration function: It allows you to call a series of functions on a receiver to configure it for use. After the lambda provided to apply executes, apply returns the configured receiver.

apply can be used to reduce the amount of repetition when configuring an object for use. Here is an example of configuring a file instance without apply:

    val menuFile = File("menu-file.txt")
    menuFile.setReadable(true)
    menuFile.setWritable(true)
    menuFile.setExecutable(false)

Using apply, the same configuration can be achieved with less repetition:

 val menuFile = File("menu-file.txt").apply { setReadable(true) setWritable(true) setExecutable(false) }  ...