Scope functions
- Kotlin course
- Intermediate
- Lesson 57/116
- 5 min
Learn let, run, apply, also and with scope functions.
Scope functions
Scope functions work on an object in a temporary scope. Kotlin has five: let, run, apply, also and with.
Example: val list = mutableListOf<Int>().apply { add(1); add(2) }. apply configures the object and returns it. Calling val s = "hi".let { it.uppercase() } returns "HI". let produces a return value; apply returns the object. Each scope function gives a different context; the right choice makes code short and readable.
apply and let
apply and let are the most common scope functions. apply suits configuration, let suits transformation.
Example: val list = mutableListOf<Int>().apply { add(1); add(2) } returns [1, 2]. val upper = "hi".let { it.uppercase() } returns "HI". Inside apply, this refers to the object; inside let, it refers to the object. Which scope function to choose depends on the goal.
Practice Using apply and let
Declare val list = mutableListOf<Int>().apply { add(1); add(2) }. Declare val upper = "hi".let { it.uppercase() }. In main call println(list) and println(upper) on separate lines.
Starter code
// list: add 1 and 2 with apply
// upper: uppercase with let
// print both in mainSample solution
val list = mutableListOf<Int>().apply { add(1); add(2) }
val upper = "hi".let { it.uppercase() }
fun main() {
println(list)
println(upper)
}Expected output
[1, 2] HI
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the scope functions
| Term | Meaning |
|---|---|
let |
Produces a return value |
run |
Runs code on the object |
apply |
Returns the object, this |
also |
Returns the object, it |
2 Which scope function configures an object and returns it?
- apply Correct answer
- run
- let
- with
Explanation: apply configures the object and returns it.
3 Complete the object with apply
val list = mutableListOf<Int>().____ { add(1); add(2) }val list = mutableListOf<Int>().apply { add(1); add(2) }Explanation: apply configures the object and returns it.