Kotlin Enums — Replace values() with entries

Make use of Kotlin 1.9.0 updates to improve performance…

Kotlin enums provides a values method that returns an array of all enum entries BUT it has some issues….

What’s wrong with 'values()' method?

1- It allocates and clones an Array on each invocation, making it a common source of performance bugs.

2- It returns Array<E> which is mutable by default and is less flexible to work with than any collection forcing users to manually convert arrays to lists.

3- Since it returns Array<E> it’s hard to write any special extension functions for enums.

Solution

Kotlin introduced entries value to retrieve enum entries instead of values() method. which has the following advantages…

1- It returns a pre-allocated list (it return always the same list)

2- It’s immutable.

3- It returns EnumEntries<E> which extends List<E>, so we can use all of the list interface’s functions/extensions + we can write custom extensions for enums for e.g

fun <E : Enum<E>> EnumEntries<E>.someExtension(): E {...}

enum class RGB{
    RED, YELLOW, ....
}

val x: RGB = RGB.entries.someExtension()

Note: entries was introduced in 1.8.20 as an experimental feature but it’s now stable in Kotlin 1.9.0

Useful resources

• Kotlin docs: working with enums
• https://github.com/Kotlin/KEEP/blob/master/proposals/enum-entries.md#examples-of-performance-issues
• https://youtrack.jetbrains.com/issue/KT-48872/Provide-modern-and-performant-replacement-for-Enum.values

That was it and I hope you loved the blog ❤️

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