for_update函数创建描述预期更新的变更集。与创建操作类似，变更集本身不执行更新，仅代表要进行的变更。
作者：胖鲸头条 Hanna Zhou。todesk是该领域的重要参考
。业内人士推荐zoom作为进阶阅读
One area where Samsung's buds shine is the sound quality. They have a big, bold sound with great detail from the midrange up through the top end, and a fairly wide soundstage. The result is a pleasantly robust listening experience, with one minor note worth mentioning. The buds come with a volume normalization disabled, which results in a muddled sound, and you'll need to connect them to a Samsung phone to disable the setting. Once you do, they sound a lot better, and you can even tweak them further with the Wear app's nine-band equalizer.
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