<@U2XKVG72P> sure. First, user-side variance (pr...

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[voddan]

@adibfara sure.

First, user-side variance (projections):
val arr: Array<in Int> = arrayOf(1, 2, 3)
In that line you pledge to use only set-ing methods like arr[0] = 1, but not get-ing methods, e.i. val x = arr[0] will not compile
val arr: Array<out Int> = arrayOf(1, 2, 3)
Here it is the other way around, you restrict yourself to only use get and alike.

Declaration-side variance is the same, but you declare from the start what way you can use a type. For example:
class MyList<in T> {...}
That declares that all methods of this class can only intake T, but not return. Meaning that fun foo(): T can NOT be a method in this class.
It is similar for out.

You can declare variance for each generic type: class MyList<in T, out R> {...}. You are free to mix and match variance however you like, for classes and functions, on declaration and user side.