Introduction to Kotlin (for Java Developers) - Cool Features - 8. Extension functions.kt

// We can add new functionality to a class without inheriting it
fun String.removeFirstLastChar() = this.substring(1, this.length-1)

class MyCoolClass {
    fun myMethod() {
        println( "hello".removeFirstLastChar() )
        println( "505".toLong() ) // Kotlin itself also gives us some extension functions
    }

    /*
        Also very useful for mapping DTOs to entities and vice-versa. Something like:

        fun UserDto.toEntity() = User(firstName = firstName, lastName = lastName)
        fun User.toDto() = UserDto(firstName = firstName, lastName = lastName)
     */
}