2.2 KiB
| title | localeTitle |
|---|---|
| True, False, and Nil | 真，假，没有 |
真，假，没有
true ， false和nil是Ruby中特殊的内置数据类型。这些关键字中的每一个都评估为一个对象，该对象是其各自类的唯一实例。
true.class
=> TrueClass
false.class
=> FalseClass
nil.class
=> NilClass
true and false are Ruby's native boolean values. A boolean value is a value that can only be one of two possible values: true or not true. The object true represents truth, while false represents the opposite. You can assign variables to true / false, pass them to methods, and generally use them as you would other objects (such as numbers, Strings, Arrays, Hashes).
nil is a special value that indicates the absence of a value: it is Ruby's way of referring to "nothing". An example of when you will encounter the nil object is when you ask for something that doesn't exist or cannot be found:
红宝石 帽子= \[“beret”，“sombrero”，“beanie”，“fez”，“flatcap”\]
帽子\[0\] =>“贝雷帽”＃索引0处的帽子 帽子\[2\] =>“豆豆”＃索引2处的帽子 帽子\[4\] =>“flatcap”＃索引4处的帽子 帽子\[5\] => nil＃在索引5处没有帽子，索引5没有任何内容（零）
Zero is not nothing (it's a number, which is something). Likewise, empty strings, arrays, and hashes are not nothing (they are objects, which happen to be empty). You can call the method nil? to check whether an object is nil.
红宝石 0.nil？ =>假 ““。零？ =>假 \[\]。零？ =>假 {}。零？ =>假 nil.nil？ =>是的 ＃来自上面的例子 帽子\[5\] .nil？ =>是的 \`\`\`
Ruby中的每个对象都有一个布尔值，这意味着它在布尔上下文中被认为是true或false。在这种情况下被认为是真实的是“真实的”，那些被认为是虚假的是“虚假的”。在Ruby中， _只有_ `false`和`nil`是“ `false`的”，其他一切都是“真实的”。
### 其他资源
* https://ruby-doc.org/core-2.3.0/TrueClass.html
* https://ruby-doc.org/core-2.3.0/FalseClass.html
* https://ruby-doc.org/core-2.3.0/NilClass.html
* https://en.wikipedia.org/wiki/Boolean