What is inline function in Kotlin?

Answer

An inline function instructs the compiler to copy the function's code and paste it directly into the call site, instead of creating a standard function call object.

Why use it?

• Performance: Reduces overhead of function calls and object allocation, especially for Higher-Order Functions (functions that take lambdas).
• Without inline, every lambda passed to a function creates an anonymous class object in Java bytecode, which costs memory.

Example

Copy codeinline fun executeOp(op: () -> Unit) {
    println("Start")
    op()
    println("End")
}

// Usage
executeOp { println("Working") }

Compiler output (conceptually):

Copy codeprintln("Start")
println("Working") // The lambda body is pasted here
println("End")

Caveat

Don't inline large functions, as it increases the bytecode size of your application.