varargs to map in Kotlin

Question

I use NamedParameterJdbcTemplate in my project and pass parameters this way:

MapSqlParameterSource(mapOf(
    "userId" to userId,
    "count" to count
))

I don't want to write the first line all the time and I want to create my own function that will take pairs of string-to-any values:

params(
    "userId" to userId,
    "count" to count
)

But when I try to implement it I have issues with generics (I don't post the error description here):

fun params(vararg pairs: Pair<String, Any>) = MapSqlParameterSource(mapOf(pairs))

Could you please advice on the correct implementation?

Answer 1

mapOf has 3 implementations: taking nothing, taking 1 pair and taking a vararg of pairs.

Since pairs in your code is actually Array<Pair<String, Any>> there is no matching implementation of mapOf to call. This is due to the fact that varargs as java implements them are ambiguous in certain cases so Kotlin requires explicit arguments.

To make it work use the "spread" operator to indicate the vararg method should be used. (https://kotlinlang.org/docs/reference/functions.html#variable-number-of-arguments-varargs)

fun params(vararg pairs: Pair<String, Any>) = MapSqlParameterSource(mapOf(*pairs))