The inline keyword tells the Kotlin compiler to replace all occurrences of calls to this function with the actual body of the function itself.

Without inline, our main() function would call this max() function normally. With inline, though, it is as if the code for max() were in main() itself:

val bigger = if (3 > 7) 3 else 7

This reduces some runtime overhead associated with calling a function. However, it increases the size of your compiled code if you call this function from lots of different places.

• the documentation