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()
}

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!

love it.

@thought-police-000 definitely love the buildString builder, i didn't know about that!

regarding the ): you could count the " as well in a "stringLevel" to decide whether one is still inside a string or to decrement the indentation level? adds complexity obviously :/