if 表达式

if 表达式 的用法与其他语言中的 if 语句完全一样。

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此外，你还可以将 if 用作一个表达式。每个块的最后一个表达式 将成为 if 表达式的值：

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Speaker Notes

 This slide should take about 4 minutes.

Because if is an expression and must have a particular type, both of its branch blocks must have the same type. Show what happens if you add ; after "small" in the second example.

如果在表达式中使用 if，则表达式中必须包含 ; 来将其与下一个语句分隔开。移除 println! 前面的 ; 即可查看编译器错误。