The closures notation strips away the boilerplate associated with inner classes, allowing a more compact (and more importantly, more direct) expression of the desired data operation.
闭包标注取消了与内部类相关的引用，允许更紧凑(重点更突出、更直接)地表示需要的数据操作。
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The splitting operation accomplished by the "\w+" expression in this case could be just as easily accomplished with the String.Split method, which would be much faster.
It says that the function must be used in an expression involving the comparison operation and that the search method "equals" of the index extension hash_index is referred to.