Switch on a Byte

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?

score 10 · Accepted Answer · edited May 23 '17 at 10:32

10

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."

edited May 23 '17 at 10:32

Community

1
1

answered Nov 19 '16 at 04:59

ruakh

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How inefficient is this if I am going to be doing this in a tight loop? – Cactus Nov 19 '16 at 05:43
You can extract `0.toByte()` into a local variable for efficiency. Not sure JIT doesn't do it already thou – voddan Nov 19 '16 at 09:59
3

`0.toByte()` is evaluated at compile time, so there's no cost of conversion at runtime. – Ilya Nov 22 '16 at 22:35

mfulton26 · Answer 2 · 2019-01-14T17:27:43.967

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
    }
}

Switch on a Byte

2 Answers2