Kotlin
inline
Learn performance optimization with inline.
inline
The inline keyword makes a function be inlined directly at the call site. It reduces the lambda creation overhead in higher-order functions.
Example: inline fun repeatN(times: Int, action: (Int) -> Unit) { for (i in 1..times) action(i) }. Calling repeatN(3) { println("Run $it") } prints three times. Thanks to inline, no lambda object is created; the code is inlined at the call site. This helps performance. But each inline function can grow code size; it is used for small functions.
The repeatN function
An inline higher-order function inlines the lambda at the call site. The action(i) call is expanded at compile time.
Example: inline fun repeatN(times: Int, action: (Int) -> Unit) { for (i in 1..times) action(i) }. Calling repeatN(3) { println("Run $it") } prints Run 1
Run 2
Run 3. it is the lambda's single parameter. inline functions are common in collection methods; forEach, map and filter are inline in the standard library.
Exercise The repeatN inline function
Define inline fun repeatN(times: Int, action: (Int) -> Unit) whose body does for (i in 1..times) action(i). In main call repeatN(3) { println("Run $it") }.
Show example solution
inline fun repeatN(times: Int, action: (Int) -> Unit) {
for (i in 1..times) action(i)
}
fun main() {
repeatN(3) { println("Run $it") }
}
Test yourself
-
What does the <code>inline</code> keyword provide?
- Hiding the function
- Pinning the function
- Recursion of the function
- Inlining the function body at the call site
Show answer
Inlining the function body at the call site — inline inlines the function body at the call site.
-
Match the inline parts
- inline fun repeatN
- inline signature
- action: (Int) -> Unit
- Function parameter
- for (i in 1..times)
- Loop
- action(i)
- Lambda call
-
Complete the inline function definition
inline ____ repeatN(times: Int, action: (Int) -> Unit) {
for (i in 1..times) action(i)
}
Show answer
inline fun repeatN(times: Int, action: (Int) -> Unit) {
for (i in 1..times) action(i)
}
Next lesson: Scope functions
