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kotlinlang

Hi!
I have:

`interface Attributes&lt;T&gt;
enum class StringAttributes : Attributes&lt;T&gt; { ... }`

`val attributes: Map&lt;Attributes&lt;Any&gt;, Any&gt;`

`val others: Map&lt;StringAttributes, String&gt; = ...`

However, if I write:

`attributes = others`

I get a `Type Mismatch`.
I guess the solution has something to do with properly using in and out, however I don't understand what the correct way to use those is.

By trial and error, I found that this works:

`interface Attributes&lt;out T&gt;`

`val attributes: Map&lt;out Attributes&lt;Any&gt;, Any&gt;`

However, I'm not completely sure I understand why that works, even after reading the documentation...

This relates to type variance.
This article explains is quite well.
 <https://link.medium.com/SjF3tlITbcb|https://link.medium.com/SjF3tlITbcb>

One thing I like to always add when trying to explain sub-types, is relating sub-types to 'assignability':
If `B` is a sub-type of `A`, then you can _safely_ assign a variable of type `B` to a variable of type `A`:
```val aB: B = ....
val anA: A = B
```
.