Data classes in Kotlin

One keyword buys equals, hashCode, toString, copy and destructuring.

// A data class writes equals, hashCode, toString and copy for you.
data class TrailLeg(val from: String, val to: String, val km: Double)

fun main() {
    val morning = TrailLeg("Aspen Gate", "Windy Col", 8.4)
    println(morning)

    // copy changes only what you name; the original is untouched.
    val rerouted = morning.copy(km = 9.7)
    println(rerouted == morning)

    val (start, end, distance) = rerouted
    println("$start to $end is $distance km")
}

How it works

1. data class TrailLeg prints itself readably with no extra code.
2. copy(km = 9.7) clones with one field changed; equality is by value.
3. val (start, end, distance) = rerouted unpacks the properties in order.

Keywords and builtins used here

• Double
• String
• TrailLeg
• class
• data
• fun
• main
• val

The run, in numbers

Lines

14

Characters to type

437

Tokens

88

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 75 seconds.

Type this snippet

Step 1 of 3 in Classes & objects, step 13 of 27 in Language basics.

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