A modern programming language that makes developers happier.

kotlinlang

Hi folks, `fold` is less performant than a loop, right?
Specifically:
```bytes.fold("") { acc, byte -&gt; acc + String.format("%02X", byte) }```
vs
```var ret: String = ""
for (b in bytes) {
    ret += String.format("%02X", b)
}
return ret```

Both of those are going to be pretty horrific because of what you're doing with the string.

Wrap it all in `buildString`, presize with `bytes.length * 2`, and append in a loop. You probably also want to avoid doing `String.format` and encode the bytes directly to chars which is must faster and doesn't allocate.

But otherwise `fold` and the loop are basically equivalent. If you CMD+B into the source of `fold` you'll just find a loop.

I found this in SO:
```private val HEX_ARRAY = "0123456789ABCDEF".toCharArray()
fun ByteArray.toHex(): String {
    val hexChars = CharArray(size * 2)
    for (j in indices) {
        val v: Int = this[j].toInt() and 0xFF
        hexChars[j * 2] = HEX_ARRAY[v ushr 4]
        hexChars[j * 2 + 1] = HEX_ARRAY[v and 0x0F]
    }
    return String(hexChars)
}```


and I see `fold` is a loop now, thanks :+1:

Yes something like that will be much more performant!