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kotlinlang

Hi! Reading on smart cast in Kotlin and came up on following statement

&gt; When you're using a smart cast with a property of a class, the property has to be a val and it can't have a custom accessor. Otherwise, it would not be possible to verify that every access to the property would return the same value.
Makes sense but one thing that I don't understand is, what does the author mean
&gt; property has to be a val and it can't have a custom accessor 
Doesn't val properties provide only getter methods?

it can’t be defined as `val someProperty get() = …`  = custom accessor

why defining it as `val someProperty get() = ...` fails to verify that the val was changed?

Because the getter could return different things depending on what the ... Is

e.g. `val someProperty: String? get() = if (System.currentTimeMillis % 2 == 0) "hello" else null` - the nullness-or-not is unpredictable