kotlin-stdlib/kotlin.text/replaceFirstChar

replaceFirstChar

@JvmName(name = "replaceFirstCharWithChar")

inline fun String.replaceFirstChar(transform: (Char) -> Char): String

@JvmName(name = "replaceFirstCharWithCharSequence")

inline fun String.replaceFirstChar(transform: (Char) -> CharSequence): String

Returns a copy of this string having its first character replaced with the result of the specified transform, or the original string if it's empty.

Since Kotlin

1.5

Samples

import samples.*
import java.util.Locale
import kotlin.test.*
fun main() { 
   //sampleStart 
   assertPrints("kotlin".replaceFirstChar { it.uppercase() }, "Kotlin")

val sentence = "Welcome to Kotlin!"
val words = sentence.split(' ');
assertPrints(words.joinToString(separator = "_") { word -> word.replaceFirstChar { it.lowercase() } }, "welcome_to_kotlin!") 
   //sampleEnd
}

Parameters

transform

function that takes the first character and returns the result of the transform applied to the character.