fun CharSequence.commonPrefixWith(
    other: CharSequence, 
    ignoreCase: Boolean = false
): String

Returns the longest string prefix such that this char sequence and other char sequence both start with this prefix, taking care not to split surrogate pairs. If this and other have no common prefix, returns the empty string.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
println("Hot_Coffee".commonPrefixWith("Hot_cocoa")) // Hot_
println("Hot_Coffee".commonPrefixWith("Hot_cocoa", true)) // Hot_Co
println("Hot_Coffee".commonPrefixWith("Iced_Coffee")) //
//sampleEnd
}

Parameters

ignoreCase - true to ignore character case when matching a character. By default false.