Hfrhyu

Consider:

val foo: Int = 1
foo.toDouble() // ok

val bar = 2.toUInt()
bar.toDouble() // error!

This doesn't make sense to me. Why wouldn't UInt have toDouble? (it also doesn't have .toFloat).

The docs say:

Every number type supports the following conversions:

• toByte(): Byte


• toShort(): Short


• toInt(): Int


• toLong(): Long


• toFloat(): Float


• toDouble(): Double


• toChar(): Char

So it should be possible. The error I get is:

Error:(11, 4) Unresolved reference. None of the following candidates is applicable because of receiver type mismatch:
@InlineOnly public inline fun String.toDouble(): Double defined in kotlin.text

Is UInt not considered a number type? Or is it something else?

Is UInt not considered a number type?

Yes, it doesn't extend Number class.

Declaration of Int:

class Int : Number, Comparable<Int>

Declaration of UInt:

inline class UInt : Comparable<UInt>

Starting with Kotlin version 1.3.30 UInt has toFloat and toDouble methods.

This appears to be coming in 1.3.30, according to this YouTrack request.

1.3.30 was just recently tagged and appears to be releasing very shortly.

Added support in latest version 1.3.30.

This release (More) brings support for more operations for unsigned types and arrays of unsigned types that mirror those for regular number types:

fun main() 
 val u1 = 2_147_483_649u
 val u2 = 4_000_000_000u
 println(u1.toDouble())
 println(minOf(u1, u2))

 val array: UIntArray = uintArrayOf(u1, u2)
 println(array.max())
 println(array.all it > Int.MAX_VALUE.toUInt() )
 

Note: UInt doesn't extend Number class.

/**
 * Converts this [UInt] value to [Double].
 *
 * The resulting `Double` value represents the same numerical value as this `UInt`.
 */
@kotlin.internal.InlineOnly
public inline fun toDouble(): Double = uintToDouble(data)