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kotlinlang

Yeah, I know those already. But neither `requireXXX` (for "check incoming arguments") nor `checkXXX` (for "check if this method may be called right now") are appropriate for an "this internal state must be like this or I made a programmer error".

Why isn’t `checkXXX` appropriate in your opinion? It throws an `IllegalStateException`, and if you look at the samples <https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/samples/test/samples/misc/preconditions.kt> they use it to check state.

If you read the Javadocs on `IllegalStateException` it becomes clear: 
&gt; Signals that a method has been invoked at an illegal or inappropriate time.
That is not the case, it was fine to invoke the method here, but something inside the method went wrong, due to a program _bug_.