Inline functions

You can think of inline functions as instructions for the compiler to copy and paste your code. Each time the compiler sees a call to a function marked with the inline keyword, it will replace the call with the concrete function body.

It makes sense to use the inline function if it's a higher-order function that receives a lambda as one of its arguments. This is the most common use case where you would like to use inline.

Let's look at such a higher-order function and see what pseudocode the compiler will output.

First, here is the function definition:

inline fun logBeforeAfter(block: () -> String) { 
    println("Before") 
    println(block()) 
    println("After") 
}

Here, we pass a lambda, or a block, to our function. This block simply returns the word "Inlining" as a String:

logBeforeAfter { 
    "Inlining" 
}

...