Number is an abstract class and does not define anything for addition. And since there's no defined method for adding the numbers, you can't do numberInstane + otherNumberInstance. You can, however, create an operator function for it:
infix operator fun Number.plus(other: Number) : Number{
return when (this) {
is Double -> this + other.toDouble()
is Int -> this + other.toInt()
is Long -> this + other.toLong()
is Float -> this + other.toFloat()
is Short -> this + other.toShort()
is Byte -> this + other.toByte()
else -> 0
}
}
Note that this only applies to addition. The rest of the functions would follow the same pattern, but replacing the operator (here it's +) and the name of the function (here it's plus).
As mer msrd0's comment, the above would result in 1 + 1.5 being 2, because it rounds down. Kotlin supports adding number types across each other, which ends up with this slightly horrid solution:
infix operator fun Number.plus(other: Number) : Number{
when {
this is Double -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
this is Int -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
this is Long -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
this is Float -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
this is Short -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
this is Byte -> {
return when(other){
is Double -> this + other
is Int -> this + other
is Long -> this + other
is Float -> this + other
is Short -> this + other
is Byte -> this + other
else -> 0
}
}
else -> return 0
}
}
The nested when-statement helps autocasting the values, which is necessary since Number isn't a specific known class. There might be a better solution though, but without knowing the specific type. The extension function is mostly just auto-casting based on the type, but there can't be a single variable because it would need to be defined as a Number to accept all the types, and since there are two vars where both need proper casting based on the passed type, it ends up being slightly messy.
