Using let() and apply()

In Kotlin, every type has a let() and apply() extension function. These are two simple but helpful tools to make your code more fluent and expressive.

Using let()

let() simply accepts a lambda that maps the invoked object T to another object R. It is similar to how RxJava offers the to() operator, but it applies to any type T and not just Observables/Flowables. For example, we can call let() on a string that has been lowercased and then immediately do any arbitrary transformation on it, such as concatenating its reversed() string to it. Take a look at this operation:

fun main(args: Array<String>) {

     val str = "GAMMA"

     val lowerCaseWithReversed = str.toLowerCase().let { it + " " +
     it.reversed() }

     println(lowerCaseWithReversed)
 }

The output is as follows:

gamma ammag

The let() comes in handy when you do not want to save a value to a variable just so you can refer to it multiple times. In the preceding code, we did not have to save the result of...