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kotlinlang

When declaring a higher order function (that accepts a lambda as argument) where you don’t use (and don’t care about) the return value of the lambda, do you put `Any?` or `Unit` for the return type? I guess `Any?` is the appropriate type, but I wonder if it adds confusion for example in private functions where you know the return type of the lambda is always `Unit`.
1. `Any?` always
2. `Unit` always
3. `Any?` when public, `Unit` when private and possible

type expression based on lambda return type,
```fun &lt;T&gt; foo(..., f : (...)-&gt;SomeTypeExpression1&lt;T&gt;) : SomeTypeExpression2&lt;T&gt;```

Unless you never use returned value, than `Unit`

2. even if the caller has a lambda that returns non-Unit, they can always wrap it `{ foo() }` when passing it on

Ok, but why not just use `Any?` so they don’t have to?

IMO your types should tell you something about what the function does. if it's only executed for the side effect, it should be marked as returning Unit. Any? might imply that the value is still used somehow.