Best Way to Convert ArrayList to String in Kotlin

Kotlin has joinToString method just for this

list.joinToString()

You can change a separator like this

list.joinToString(separator = ":")

If you want to customize it more, these are all parameters you can use in this function

val list = listOf("one", "two", "three", "four", "five")
println(
    list.joinToString(
        prefix = "[",
        separator = ":",
        postfix = "]",
        limit = 3,
        truncated = "...",
        transform = { it.uppercase() }
    )
)

which outputs

[ONE:TWO:THREE:…]