What have I done wrong: ```private fun <Long&gt...

# announcements

[Martin Barth]

What have I done wrong:

private fun <Long> List<Long>.combinationSums(): Sequence<Long> {
    val list = this
    return sequence {
        for (i in 0 until list.count()) {
            for (j in i + 1 until list.count()) {
                val sum: Long = list[j] + list[i]
                yield(sum)
            }
        }
    }.distinct()
}

I am getting a compiler error for the `list[i] + list[j]:

Unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 
public inline operator fun BigDecimal.plus(other: BigDecimal): BigDecimal defined in kotlin
public inline operator fun BigInteger.plus(other: BigInteger): BigInteger defined in kotlin
public operator fun <T> Array<TypeVariable(T)>.plus(element: TypeVariable(T)): Array<TypeVariable(T)> defined in kotlin.collections

[jbnizet]

You made the function generic, and instead of choosing the usual <T> or <R> or whatever for the generic type, you chose <Long>. So, in your code, Long means: some generic type which could be anything. Remove the <Long> after `private fun`: your method shouldn’t be generic.

[Martin Barth]

ah!

[Martin Barth]

thank you!

[nkiesel]

Happy Advent of Code! BTW: my solution uses

fun notSum(v: Long, l: List<Long>): Boolean {
    val s = l.toSet()
    return l.none { v != it * 2 && s.contains(v - it) }
}

[Martin Barth]

👍