is there some kind of trick to understand this low...

# announcements

[torres]

is there some kind of trick to understand this low level kotlin syntax ? I dont understand what is Key, T and * in here

fun <Key:Comparable<Key>, T: IdTable<Key>> T.insertIgnoreAndGetId(body: T.(UpdateBuilder<*>)->Unit) = InsertStatement<EntityID<Key>>(this, isIgnore = true).run {
    body(this)
    execute(TransactionManager.current())
    getOrNull(id)
}

[torres]

from https://github.com/JetBrains/Exposed/blob/b983784bddd0441a9fcd7c6f5bbd5cc7424142d1/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Queries.kt#L148

[Jakub Pi]

Key and T are generic parameters with restrictions that Key must implement Comparable and T must be of type IdTable.. The next part makes this function an extension on T. The <*> just means it will accept any UpdateBuilder regardless of parameter type, or in this case any function reference on T that takes an UpdateBuilder parameter and returns Unit.

[Zach Klippenstein (he/him) [MOD]]

Not sure what you mean by "low-level". Those things are generic type parameters, which is a core kotlin feature that is used by kotlin code all the time: https://kotlinlang.org/docs/tutorials/kotlin-for-py/generics.html

[Evan R.]

To pull it out piece by piece…

• <Key:Comparable<Key>, T: IdTable<Key>> are the generic type parameters. They assert that Key implements comparable against itself, and T implements IdTable<Key>
• T.insertIgnoreAndGetId defines the method as an extension function on T, the table
• body: T.(UpdateBuilder<*>)->Unit means the parameter, body accepts a function returning Unit which is either an extension or member of T that gets passed a parameter of type UpdateBuilder<*>, where `UpdateBuilder`’s generic type doesn’t matter (it’s a wildcard)
• = InsertStatement<EntityID<Key>>(this, isIgnore = true).run { means this is a single-expression function, returning the result of InsertStatement.run(). It constructs an insert statement and runs the “run” block, returning the “run” block’s value
• body(this) executes the function passed as a parameter, using this (the insert statement) as the parameter and receiver
• execute(TransactionManager.current()) is calling InsertStatement.execute() on the current transaction manager to perform the SQL query
• getOrNull(id) is executing InsertStatement.getOrNull() to retrieve the value of the id column from the result. As this is the last statement in the “run” block, either the value of the ID column is returned, or Null on an error
Hope that helped! And I highly recommend checking out the resources that other users posted above.