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## Refutability(可反驳性): 模式是否会匹配失效 ## Refutability(可反驳性): 模式是否会匹配失效
模式有两种形式: refutable(可反驳)和irrefutable(不可反驳). 对任意可能的值进行匹配都不会失效的模式被称为是*irrefutable*(不可反驳)的, 而对某些可能的值进行匹配会失效的模式被称为是*refutable*(可反驳)的. 匹配模式有两种形式: refutable(可反驳)和irrefutable(不可反驳). 对任意可能的值进行匹配都不会失效的模式被称为是*irrefutable*(不可反驳)的, 而对某些可能的值进行匹配会失效的模式被称为是*refutable*(可反驳)的.
`let` statements, function parameters, and `for` loops are restricted to only `let`语句、 函数参数和`for`循环被约束为只接受*irrefutable*模式, 因为如果模式匹配失效程序就不会正确运行. `if let`和`while let`表达式被约束为只接受*refutable*模式, 因为它们需要处理可能存在的匹配失效的情况, 并且如果模式匹配永不失效, 那它们就派不上用场了.
accept irrefutable patterns, since there's nothing correct the program could do
if the pattern fails to match. `if let`, and `while let` expressions are
restricted to only accept refutable patterns, since they're made to handle
possible failure and we wouldn't need their functionality if the pattern could
never fail.
In general, you shouldn't have to worry about the distinction between refutable 通常, 你不用关心*refutable*和*irrefutable*模式的区别, 当你看见它出现在了错误消息中时, 你只要了解*可反驳性*(refutability)的概念即可. 如果你得到一个涉及到可反驳性概念的错误消息, 根据你的代码行为的意图, 你只需改变匹配模式或者是改变你构造模式的方法即可.
and irrefutable patterns; just be familiar with the concept of refutability
when you see it mentioned in an error message. When you get an error message
involving refutability, you'll need to change either the pattern or the
construct you're using the pattern with, depending on your intentions for the
behavior of the code.
Let's look at some examples. Earlier in this chapter, we had `let x = 5;`. `x` 让我们来看几个例子. Earlier in this chapter, we had `let x = 5;`. `x`
is indeed an irrefutable pattern we're allowed to use: since it matches is indeed an irrefutable pattern we're allowed to use: since it matches
anything, it can't fail to match. In contrast, consider trying to match one anything, it can't fail to match. In contrast, consider trying to match one
variant of an enum with `let`, such as matching only a `Some<T>` value from the variant of an enum with `let`, such as matching only a `Some<T>` value from the