Alternatives to implicit conversion, lifting String to Expr type

I have some code that builds up SQL expressions. I created a group of sealed classes.

sealed class SqlExpr
class SqlPiece(val sql: String) : SqlExpr()
class SqlAnd(vararg parts: SqlExpr) : SqlExpr()

It would be nice to write something like:

SqlAnd("x", someExpr, "foo is null", otherExpr)

instead of:

SqlAnd(SqlPiece("x"), someExpr, SqlPiece("foo is null"), otherExpr)

In some languages I could declare that Strings are SqlExprs. In others I could declare an implicit conversion from String to SqlPiece. Any recommended style for this situation in Kotlin?

In Java, you’d probably create an overload with Object... vararg type and convert the instances appropriately. You don’t even need to throw an exception for anything that isn’t String or SqlExpr, you could just call toString on everything that isn’t an SqlExpr and wrap that resulting String (which would also allow you to pass String-like classes like StringBuilder).

I’d guess in Kotlin you can do the same with varargs parts: Any.

I may just use that. While not as perfectly type-safe, in practice it’s useful.

I also forgot, an extension property or method on String is another option…

SqlAnd("x".toSql(), someExpr, ...)
SqlAnd("x".sql, someExpr, ...)