Switch on a Byte - switch-statement

Question

How can I switch on a Byte value? The obvious way would be:
fun foo(b: Byte): Boolean {
return when(b) {
0 -> true
else -> false
}
}
but that fails at compile time with
src/ByteSwitch.kt:3:5: error: incompatible types: kotlin.Int and kotlin.Byte
0 -> true
^
Is there a way to make that 0 be a byte literal?

Answer 1

Since Kotlin allows branch conditions to be arbitrary expressions (not necessarily constants), one approach is to accept that the 0 will be an Int and simply convert it explicitly to a Byte:
fun foo(b: Byte): Boolean {
return when(b) {
0.toByte() -> true
else -> false
}
}
Per Ilya, "0.toByte() is evaluated at compile time, so there's no cost of conversion at runtime."

Answer 2

You cannot specify a byte literal in Kotlin (nor can you in Java). From Literal Constants - Basic Types - Kotlin Programming Language
There are the following kinds of literal constants for integral
values:
Decimals: 123
Longs are tagged by a capital L: 123L
Hexadecimals: 0x0F
Binaries: 0b00001011
You can however declare compiler-time constants to avoid run-time overhead:
const val ZERO_BYTE: Byte = 0
fun foo(b: Byte): Boolean {
return when (b) {
ZERO_BYTE -> true
else -> false
}
}
Inspecting the Kotlin bytecode further reveals that as 0.toByte() can be determined at compile-time you can in fact inline the evaluation with no additional run-time overhead:
fun foo(b: Byte): Boolean {
return when (b) {
0.toByte() -> true
else -> false
}
}