Using what are called facets, you can derive new types that represent a smaller subset of values of some other types, for example, to define a subset by enumeration, range, or pattern matching.

使用所谓的facets，您可以派生新的类型，表示其他某个类型值的更小子集，比如通过枚举、范围或模式匹配来定义子集。

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This looping construct is used to iterate over the matches of a pattern in an enumerable collection such as a range expression, sequence, list, array, or other construct that supports enumeration.

此循环构造用于循环访问可枚举集合(例如，范围表达式、序列、列表、数组或其他支持枚举的构造)中的模式匹配项。

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