Kotlin 2.4 Collection Literals and Type Inference

Mon, 08 Jun 2026 10:46:24 +0900

Kotlin 2.4 introduces experimental support for collection literals, allowing collections to be created using square brackets.

Experimental Support for collection literals

Support for collection literals Kotlin 2.4.0 introduces experimental support for collection literals. You can now create collections in a simpler and more concise way using brackets [].

https://kotlinlang.org/docs/whatsnew24.html#support-for-collection-literals

kotlin {
    jvmToolchain(21)
    compilerOptions {
         freeCompilerArgs.add("-Xcollection-literals")
    }
}

Let’s compare the inferred types of several common collection APIs.

val names = mutableListOf("Joe", "Alice")
// MutableList<String>

val names = listOf("Joe", "Alice")
// List<String>

val names = listOf("Joe", "Alice").toMutableList()
// MutableList<String>

val names = arrayOf("Joe", "Alice")
// Array<String>

With collection literals enabled:

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Kotlin 2.4 Collection Literals and Type Inference