Pretty Print Kotlin Data Class

PrettyPrint.kt

fun Any.prettyPrint(): String {

    var indentLevel = 0
    val indentWidth = 4

    fun padding() = "".padStart(indentLevel * indentWidth)

    val toString = toString()

    val stringBuilder = StringBuilder(toString.length)

    var i = 0
    while (i < toString.length) {
        when (val char = toString[i]) {
            '(', '[', '{' -> {
                indentLevel++
                stringBuilder.appendLine(char).append(padding())
            }
            ')', ']', '}' -> {
                indentLevel--
                stringBuilder.appendLine().append(padding()).append(char)
            }
            ',' -> {
                stringBuilder.appendLine(char).append(padding())
                // ignore space after comma as we have added a newline
                val nextChar = toString.getOrElse(i + 1) { char }
                if (nextChar == ' ') i++
            }
            else -> {
                stringBuilder.append(char)
            }
        }
        i++
    }

    return stringBuilder.toString()
}

That's great @odonckers ! Glad it helped. I remember implementing a custom serializer using Kotlinx serialization to achieve the same. It was hacky and dirty but sufficed my use case. This is much easier and can be useful in many places. Awesome work!

FWIW, this fails to produce a pretty output if you have strings that contain the , character

I cut this back and cleaned it up a little, and added some kotliny goodness, to make it a little cleaner and easier to read.

fun Any.pretty() = toString().let { toString ->
    var indentLevel = 0
    val indentWidth = 4
    var i = 0
    fun padding() = "".padStart(indentLevel * indentWidth)
    buildString {
        var ignoreSpace = false
        toString.onEach { char ->
            when (char) {
                '(', '[', '{' -> {
                    indentLevel++
                    appendLine(char)
                    append(padding())
                }

                ')', ']', '}' -> {
                    indentLevel--
                    appendLine()
                    append(padding())
                    append(char)
                }

                ',' -> {
                    appendLine(char)
                    append(padding())
                    ignoreSpace = true
                }
                ' ' -> {
                    if (!ignoreSpace) append(char)
                    ignoreSpace = false
                }

                else -> append(char)
            }
        }
    }
}

With this method I don't think there's any way to get around a string containing a closing bracket.

data class Fish(val message: String)

Fish("bobby),otherValue=fakeData").pretty()

@thought-police-000 Thanks for sharing your awesome code!