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引用部分の読みやすさ改善のため、Markdownを付加
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[ios - How do I catch "Index out of range" in Swift? - Stack Overflow](https://stackoverflow.com/questions/37222811/how-do-i-catch-index-out-of-range-in-swift)には以下のようなコメントがありました。
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※読みやすさを重視して、引用部分にオリジナルのコメントに似せたMarkdownを付加しました。
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> Swift's [Error Handling](https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/ErrorHandling.html) (do/try/catch) is **not** the solution to **runtime exceptions** like "index out of range".
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> A runtime exception (you might also see these called trap, fatal error, assertion failure, etc.) is a sign of programmer error. Except in -Ounchecked builds, Swift usually guarantees that these will crash your program, rather than continuing to execute in a bad/undefined state. These sorts of crashes can arise from force-unwrapping with !, implicit unwrapping, misuse of unowned references, integer operations/conversions which overflow, fatalError()s and precondition()s and assert()s, etc. (And, unfortunately, Objective-C exceptions.)
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> A runtime exception (you might also see these called __trap__, __fatal error__, __assertion failure__, etc.) is a sign of programmer error. Except in `-Ounchecked` builds, Swift usually guarantees that these will **crash** your program, rather than continuing to execute in a bad/undefined state. These sorts of crashes can arise from force-unwrapping with `!`, implicit unwrapping, misuse of `unowned` references, integer operations/conversions which overflow, `fatalError()`s and `precondition()`s and `assert()`s, etc. (And, unfortunately, Objective-C exceptions.)
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> The solution is to simply avoid these situations. In your case, check the bounds of the array:
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> The solution is to simply **avoid these situations**. In your case, check the bounds of the array:
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> ```
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if indexPath.section < msgSections.count && indexPath.row < msgSections[indexPath.section].msg.count {
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let msg = msgSections[indexPath.section].msg[indexPath.row]
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// ...
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}
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```
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> (Or, as rmaddy says in comments — investigate why this problem is occurring! It really shouldn't happen at all.)
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> (Or, as rmaddy says in comments — investigate **why** this problem is occurring! It really shouldn't happen at all.)
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