blocks|key|556051|text|以防止未定义的行为。如果你想用一个属性做一些事情，你希望它包含一些东西。如果它在这一点上意外为空，您应该意识到这一点，并采取相应的行动。当尝试使用nil做一些事情时，可能会出现这种情况(如果应用程序没有崩溃)，整个流程可能会停滞不前。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|556052|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

To prevent undefined behaviour. If you want to do something with a property, you expect it to contain something. And if it's accidentally nil at that point you should be aware of it and act accordingly. There might be cases when trying to do something with a nil (if the app doesn't crash), the whole flow could just stuck.

blocks|key|2598618|text|简单地说：你不希望你的应用程序崩溃。当您可能需要或可能不需要值，但您希望将变量分配给某个类型以防万一时，可选函数非常有用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2598619|这类似于骑自行车时戴头盔。你可能会在旅途中摔倒，也可能不会跌倒(赋值)，但如果你跌倒了，你肯定会很高兴为这种情况准备了头盔(准备了一个变量)。现在，如果你没有跌倒并发现头盔无用(找到nil)，你只需继续踩(+nil值的句柄)。这是我们在代码中倾向于做的事情。如果我们找到一个nil值，我们会相应地处理它，这样程序就不会崩溃。|CODE|2598620|在Swift中，有许多方法可以处理nil返回值。其中一些技术包括但不限于：|2598621|2598622|Nil+Coalescing|unordered-list-item|2598623|Guard+Statement|2598624|If+let+Conditional|2598625|2598626|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/BasicOperators.html|1|http://nshipster.com/guard-and-defer/|2|https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/OptionalChaining.html^0|0|5|0|2J|3|2W|3|3T|3|0|H|3|0|0|0|E|0|0|0|F|1|0|0|I|2|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|18|8|@$9|19|A|1A|B|H]|$9|1B|A|1C|B|H]|$9|1D|A|1E|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|1F|8|@$9|1G|A|1H|B|H]]|D|@]|E|$]]|$1|K|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1J|8|@]|D|@$9|1K|A|1L|1|1M]]|E|$]]|$1|O|3|P|5|N|7|1N|8|@]|D|@$9|1O|A|1P|1|1Q]]|E|$]]|$1|Q|3|R|5|N|7|1R|8|@]|D|@$9|1S|A|1T|1|1U]]|E|$]]|$1|S|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]|11|$5|W|X|Y|E|$Z|12]]|13|$5|W|X|Y|E|$Z|14]]]]

Simply put: you wouldn't want your application to crash. Optionals are great for when you may or may not need a value, but you want to assign a variable to a type just in case. 

It's similar to wearing a helmet when riding a bike. You may or may not fall during your ride (assign a value), but if you do, you sure will be happy that you've got a helmet (prepared a variable) for the situation. Now if you don't fall and find the helmet useless (find <code>nil</code>), you simply keep pedaling on (handle for <code>nil</code> value). This is what we tend to do in code. If we find a <code>nil</code> value, we handle it accordingly so the program doesn't crash.

There are many ways to handle a <code>nil</code> returned value in Swift. Some of these techniques include, but aren't limited to:

<ul>
<li><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/BasicOperators.html" rel="nofollow">Nil Coalescing</a></li>
<li><a href="http://nshipster.com/guard-and-defer/" rel="nofollow">Guard Statement</a></li>
<li><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/OptionalChaining.html" rel="nofollow">If let Conditional</a></li>
</ul>

blocks|key|2598641|text|解包Optional意味着获取optional中的(非nil)值。如果optional包含nil，那么崩溃是非常正确的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2598642|有几种方法可以有条件地展开可选值|2598643|例如。|2598644|let+name:+String?+=+nil|code-block|syntax|javascript|2598645|如果让，则|2598646|if+let+name+=+name+{
++++print(name)
}|2598647|守卫让|BOLD|2598648|guard+let+name+=+name+else+{+return+}
print(name)|2598649|内联条件|2598650|name?.uppercaseString|2598651|entityMap^0|19|3|0|0|0|0|0|0|0|3|0|0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|17|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|18|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|19|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1A|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1B|8|@$9|1C|A|1D|B|U]]|D|@]|E|$]]|$1|V|3|W|5|L|7|1E|8|@]|D|@]|E|$M|N]]|$1|X|3|Y|5|6|7|1F|8|@$9|1G|A|1H|B|U]]|D|@]|E|$]]|$1|Z|3|10|5|L|7|1I|8|@]|D|@]|E|$M|N]]|$1|11|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|12|$]]

Unwrapping an optional means getting the (non nil) value inside the Optional. If the optional contains <code>nil</code> then the crash is pretty correct.

There are several ways to conditionally unwrap an optional value

E.g.

<pre><code>let name: String? = nil
</code></pre>

if let

<pre><code>if let name = name {
 print(name)
}
</code></pre>

guard let

<pre><code>guard let name = name else { return }
print(name)
</code></pre>

inline conditional

<pre><code>name?.uppercaseString
</code></pre>

I know Swift has a rule that says if you try to unwrap an Optional that contains a <code>nil</code>, it crashes. 

Just a thought, if I want a type to be Optional (allow <code>nil</code> or a value), why would I want my program to crash if I unwrap it even if I explicitly say <code>nil</code> is allowed for my type?

Unwrapping optionals causing crash seem counter intuitive

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我知道Swift有一条规则，如果你试图解开包含nil的可选，它就会崩溃。这只是一个想法，如果我想要一个类型是可选的(允许nil或一个值)，为什么我想要我的程序在解开它时崩溃，即使我显式地说我的类型允许nil？

问解包导致崩溃的可选函数似乎有悖于直觉
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问解包导致崩溃的可选函数似乎有悖于直觉EN