Java Void type without?

Language Design
1

I just got a null pointer waring because the use of Void in a generic callback function.

Let’s say I’m using AsyncTask<Void, Void, Void> this would inherently be an error which is triggered when onPostExecute is executed since Void will always be null.

It would be great if a warning could be triggered when using Void without ? since this would always be an error, alternatively being able to drop the argument in the callbacks which are Void completely like

override fun onPostExecuteEx(dummy: Void?)  {}

override fun onPostExecuteEx()  {}

What do you think?

Also the automatic code converter should always add ? when converting java code to kotlin code for Void types

2

I’m not sure whether you need Void for Java compatibility here, but the Kotlin way would be to use Unit instead.

3

Looks like Void in java is more like Nothing in Kotlin (than Unit).
Void? has only one instance - null (same with Noting?).
Void itself has no instances at all (same with Nothing).
Unit - has only one value too Unit, but Unit? has two values (null and Unit)

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