What Kotlin feature is used for ``` object Users :...

# announcements

[rrader]

What Kotlin feature is used for

object Users : Table() {
    val id = varchar("id", 10).primaryKey() // Column<String>
    val name = varchar("name", length = 50) // Column<String>
    val cityId = (integer("city_id") references Cities.id).nullable() // Column<Int?>
}
Users.insert {
            it[id] = "andrey"
            it[name] = "Andrey"
            it[cityId] = saintPetersburgId
        }

how compiler know that it[id] is valid and for example it[title] is not valid?
from https://github.com/JetBrains/Exposed

[reik.schatz]

maybe ask in #C0CG7E0A1 but it looks like .insert is an extension function and then id, name and cityId are just Column instances given to the InsertStatement

[reik.schatz]

and val title: Column<?> just doesn’t exists in your Users object

[rrader]

but how it knows that columns are from Users and not from other object ?

[reik.schatz]

because .insert is added to Users

[reik.schatz]

fun <T:Table> T.insert(body: T.(InsertStatement<Number>)->Unit): InsertStatement<Number> = InsertStatement<Number>(this).apply {
    body(this)
    execute(TransactionManager.current())
}

[reik.schatz]

T is a specific type

[reik.schatz]

again, I am new to Kotlin. ask in #C0CG7E0A1 🙂

[rrader]

ok, thanks

[Mike]

@rrader insert is an extension function on all types. body is a Lambda with receiver. Some more advanced Kotlin features that allow for powerful DSL’s.

Hopefully those keywords give you some direction for research.

But ultimately, the Lambda you’re passing to insert (everything inside the {}) has a single parameter it that is of the type of the class insert is being called on.

So in this case, the compiler knows that it is of type Users