Convert JSON Arrays to Kotlin Lists

JSON Arrays to Kotlin Lists

JSON arrays map to Kotlin's List<T> type. The element type is inferred from the array contents -- string arrays become List<String>, object arrays become List<SomeDataClass>.

Primitive Arrays

{
  "tags": ["kotlin", "android", "api"],
  "scores": [95, 87, 92]
}

data class Response(
    val tags: List<String>,
    val scores: List<Int>
)

Array of Objects

{
  "users": [
    { "id": 1, "name": "Alice" },
    { "id": 2, "name": "Bob" }
  ]
}

data class Response(
    val users: List<User>
)

data class User(
    val id: Int,
    val name: String
)

Empty Arrays

Empty JSON arrays ([]) are ambiguous -- the converter cannot determine the element type. Most converters default to List<Any>. You should manually set the correct type once you know the expected data.

Nested Arrays

Arrays of arrays ([[1,2],[3,4]]) become List<List<Int>> in Kotlin. This pattern appears in matrix data, coordinate pairs, and batch operations.

List vs MutableList

The converter generates List<T> (immutable) by default. If you need to modify the collection after deserialization, change it to MutableList<T>:

data class Response(
    val users: MutableList<User>
)

Iterating Over Results

response.users.forEach { user ->
    println("User ${user.id}: ${user.name}")
}

// Or with destructuring
response.users.forEach { (id, name) ->
    println("User $id: $name")
}

Kotlin's destructuring works with data classes automatically, making list iteration concise and readable.