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kotlingenericsinfix-notation

Kotlin infix function with generics

Try to write a simple Kotlin infix function for plus operation. What's wrong with generic type?

infix fun <T : Number> T.myPlus(that: T): T = this + that
Solution

  • As others have mentioned, there's no solutions using generics for various reasons. You have to define an extension function for each Number type (Byte, Short, Int, Long, Float, Double). E.g. for Int you could do:

    when (that) {
    is Byte, is Short, is Int, is Long -> that.toLong().plus(this)
    is Float -> that + this
    is Double -> that + this
    else -> throw Exception("Types mismatch")
}

    Even doing that, in some cases you need to decide whether you want to truncate or round the result.

    val n1 = 1230000000000000000L
val n2 = 123.7

    This case (n1 is a Long, n2 is a Float) could be handled like this:

    is Float -> this + that.toLong()

    resulting in 1230000000000000123

    or it could be handled like this:

    is Float -> this.toFloat() + that

    resulting in 1.23E18