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<div style="font-family:monospace" class="gmail_default">More specifically, we enforce pattern dominance in switch patterns by ensuring that the pattern above is not unconditional for the pattern below.<br class="">
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<div>Essentially yes, though its more subtle than that. But where unconditionality is really important is in nesting. Suppose I have</div>
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<div> record Box(Object o) { … }</div>
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<div>and</div>
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<div> switch (box) { </div>
<div> case Box(Object o): B;</div>
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<div> case Box b: // dead</div>
<div> }</div>
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<div>We can conclude the second pattern is dominated because not only is there a “case Box(…)” above it, but the pattern nested inside it (Object o) is unconditional on the component of Box. If the first pattern were `case Box(Integer i)`, the `case Box b`
would not be dead. </div>
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<div style="font-family:monospace" class="gmail_default">And we can enforce exhaustiveness by making sure the final pattern in switch patterns is the only one that is unconditional on the parameter.<br class="">
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<div>That’s one way to get exhaustiveness, but not the only way. If I have a sealed type A = B|C, then if the switch exhausts B and C, then it exhausts A, even without any sort of `case A` pattern. </div>
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<div style="font-family:monospace" class="gmail_default">It sounds like the creases have been ironed out at this point between instanceof pattern matching and unconditionality. So why does the warning still exist for instanceof pattern matching?<br class="">
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<div>As I said, the warning is confusingly worded, and will go away when we exit preview (which is hopefully soon.)</div>
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