这些 trait 支持在值之间进行比较。对于包含实现这些 trait 的字段，可以派生所有这些 trait。
PartialEq 指部分等价关系，其中包含必需的方法 eq 和提供的方法 ne。== 和 != 运算符会调用这些方法。
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Eq is a full equivalence relation (reflexive, symmetric, and transitive) and implies PartialEq. Functions that require full equivalence will use Eq as a trait bound.
PartialOrd 定义了使用 partial_cmp 方法的部分排序。它用于实现 <、<=、>= 和 > 运算符。
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Ord 是总排序，其中 cmp 返回 Ordering。
Speaker Notes PartialEq 可以在不同类型之间实现，但 Eq 不能，因为它具有自反性：
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在实践中，派生这些 trait 很常见，但很少会实现它们。