In many programming environments it will be possible to check in experimental code in such a way that no one except the author is affected by it.
许多编程环境是允许提交试验性代码的,这种代码除了提交者本人外不会影响任何人。
Similarly, it is not possible to tell if an address field is timely if there is no check against an address Modification Date field.
类似地,如果没有检查一个Address Modification Date字段,那么就不能说一个地址字段是否是及时的。
Since there are no compile-time checks possible, there are three ways for an observable to check that Observer.update exists.
因为没有编译时期检查机制,有三种方式可以检查observer . update的存在。
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