遍历 Result

Iter::map 操作可能会失败，例如：

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让我们逐步介绍处理这种情况的策略。

使用 filter_map() 忽略失败的项

filter_map 调用一个函数并过滤掉结果为 None 的项。

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使用 map_err() 和 filter_map() 收集失败的项

map_err 会对错误调用一个函数，因此将其添加到之前的 filter_map 解决方案中，我们可以在迭代时将错误项保存到一旁。

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使用 collect() 使整个操作失败

Result 实现了 FromIterator trait，因此结果的向量（Vec<Result<T, E>>）可以转换为包含向量的结果（Result<Vec<T>, E>）。一旦遇到 Result::Err，迭代就会终止。

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这种技巧同样适用于 Option。

使用 partition() 收集所有有效值和失败项

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当你查看结果时，你会注意到所有内容仍然被包装在 Result 中。这需要一些额外的样板代码。

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