What are inline functions used for in programming?

To reduce overhead costs of function calls (creating stack frames, passing parameters, etc.), the compiler inserts the code of such a function directly at the call site. This can increase the code size but improve performance.

In Kotlin, inline functions are often used to optimize lambdas:

// without inline, the lambda becomes an object, a class is created
fun notInline(block: () -> Unit) {
    block()
}

// with inline, the lambda code is inserted at the call site
inline fun inlineExample(block: () -> Unit) {
    block()
}

fun main() {
    notInline {
        println("This is not inline")
    }

    inlineExample {
        println("This is inline")
    }
}

Usage is limited due to potential increase in APK size. Not recommended for large functions.