Use Kotlin function reference in HOF example

[russellbanks]

Having a lambda inside a function's parantheses isn't hugely idiomatic in Kotlin.

Therefore, you can either use a function reference or have it outside the parantheses:

• transform(String::uppercase)
• transform { it.uppercase() }

You don't need to specify a variable name when using a lambda as it is implicitly provided.

toUpperCase() was deprecated in Kotlin 1.5.0 in favour of uppercase().

Before:

fun transform(initial: String, f: (String) -> String) = f(initial)

val result = transform("hello", { x -> x.toUpperCase() })
// HELLO

// Trailing lambda can be placed outside the parentheses
val result2 = transform("hello") { x -> x.toUpperCase() }

After:

fun transform(initial: String, transformer: (String) -> String) = transformer(initial)

// Function reference
val result = transform("hello", String::uppercase)
// HELLO

// Trailing lambda can be placed outside the parentheses
val result2 = transform("hello") { it.uppercase() }

You can test this code here on the Kotlin Playground.

[ttu]

Thanks for the update! We could make small changes to example functions.

[ttu]

Naming function with a single letter (f) is not the best practice. However, it was used to ensure the code would fit to a single view.

[ttu]

Perhaps, from the example's perspective, changing the functionality slightly, e.g. to { "PREFIX_${it.uppercase()}" }, would make more sense. The point is not to showcase the shortest example, but to demonstrate how functions are used. I can make the corresponding change to the C# example later to match with this modification.