In this article we'll explore some advanced topics related to hashing in Kotlin, including how to hash collections, best practices, and common pitfalls.
When working with collections in Kotlin, it's often necessary to hash them in order to produce a consistent and repeatable result. There are a few different ways to go about this, depending on your needs.
If you have a list of items that need to be hashable, you can use the hashCode()
function defined on the Any
class. This will produce a 32-bit integer hash code for any object, including collections:
val list = listOf(1, 2, 3)
val hashCode = list.hashCode() // produces -1292745640
If you need to produce a hash code that's compatible with Java's Object.hashCode()
method, you can use the contentHashCode()
function defined in the Kotlin standard library:
val list = listOf(1, 2, 3)
val hashCode = list.contentHashCode() // produces 3
This function is equivalent to Java's Objects.hashCode(Object...)
method, and produces a hash code that's compatible with Java's hashCode()
method.
If you need to produce a hash code that's compatible with the hash()
function defined in the Kotlin standard library, you can use the contentDeepHashCode()
function:
val list = listOf(1, 2, 3)
val hashCode = list.contentDeepHashCode() // produces -1548664399
This function is equivalent to Kotlin's hash(vararg objects: Any?)
function, and produces a hash code that's compatible with Kotlin's hashCode()
function.
When working with hashes, there are a few best practices to keep in mind:
There are a few common pitfalls to avoid when working with hashes: