Kotlin Blueprints

Inline function

If you paid attention to our previous chapter, you will remember that we discussed Standard.kt file and functions. All those functions are inline. Inline function means replacing the body of the function at the time of building the file. It's not an actual function call. 

Using higher-order functions (https://kotlinlang.org/docs/reference/lambdas.html) imposes certain runtime penalties—each function is an object, and it captures a closure, that is, those variables that are accessed in the body of the function. Memory allocations (both for function objects and classes) and virtual calls introduce runtime overhead.

But it appears that in many cases this kind of overhead can be eliminated by inlining the lambda expressions. The ...