UUID Utilities

Kore includes a robust implementation for Universally Unique Identifiers (UUID) that works seamlessly across all Kotlin Multiplatform targets.

Supported Versions

Currently, Kore supports two versions of UUIDs:

UUID V4: Randomly generated identifiers. Best for general-purpose unique IDs where ordering is not important.
UUID V7: Time-ordered identifiers. Recommended for database primary keys as they are sortable by creation time, which improves indexing performance.

Usage

Generating UUIDs

You can generate new UUIDs using the Uuid companion object:

import com.davils.kore.uuid.Uuid

val v4 = Uuid.randomUuidV4()
val v7 = Uuid.randomUuidV7()

Working with UUIDs

All UUID classes inherit from the abstract Uuid class, which provides standard functionality:

Comparison: UUIDs are Comparable, allowing them to be sorted.
Equality: Overridden equals and hashCode based on the UUID string value.
String Representation: Use .toString() or the .value property to get the standard hyphenated string format.
Property Delegation: UUIDs can be used as property delegates.

val id = Uuid.randomUuidV7()
val stringId: String by id // stringId will be the UUID string

Why UUID V7?

Traditional UUID V4 identifiers are random, which causes "index fragmentation" in B-tree based databases when used as primary keys. New records are inserted at random locations in the index, leading to frequent page splits and poor performance.

UUID V7 solves this by including a millisecond-precision timestamp in the first 48 bits. This makes them monotonically increasing (mostly), allowing databases to append new records to the end of the index, which is significantly more efficient.

Validation

Kore automatically validates the format of UUIDs during construction. If you attempt to create a UUID from an invalid string, an IllegalArgumentException will be thrown.

07 May 2026