Here is some code which does not work. I suspect ...

# getting-started

[Alec Muffett]

Here is some code which does not work. I suspect that the reason that it does not work is that this in the buildString lambda does not refer back to the ByteArray, but instead to the implicit StringBuilder which is being built, and I suspect that the forEach is inheriting its iterator from the inner this, rather than the (shadowed) outer this.

HOWEVER: the code is cute, and I would like understand the problem to be certain, and to save the situation. Can I elegantly fix the shadowing problem in the existing code, rather than refactoring it to use a loop, or with or apply?

const val INT_TO_HEX = "0123456789ABCDEF"
fun ByteArray.toHexStringDoesNotWork() = buildString {
    forEach {
        val octet = it.toInt()
        append(INT_TO_HEX[octet.and(MASK_UPPER_NIBBLE).ushr(4)])
        append(INT_TO_HEX[octet.and(MASK_LOWER_NIBBLE)])
    }
}

[Alec Muffett]

This works but can it be made more elegant?

fun ByteArray.toHexString(): String {
    val src = this
    return buildString {
        src.forEach {
            val octet = it.toInt()
            append(INT_TO_HEX[octet.and(MASK_UPPER_NIBBLE).ushr(4)])
            append(INT_TO_HEX[octet.and(MASK_LOWER_NIBBLE)])
        }
    }
}

[Adam Powell]

Try [e-mail]

[Alec Muffett]

Awesome! That works. Thank you @Adam Powell

[Adam Powell]

The same thing works any time you need to clarify a specific this in scope

[Vampire]

Or simply

fun ByteArray.toHexString() = joinToString("") { it.toString(16).padStart(2, '0') }

🙂