so long是“再见”的非正式表达，因为它的直译是“就这么长吧”，表示在一起的时间到此为止，类似中文中的就这样吧。再见，如果直译的意思就是很久，这么久。
so long
英 [səʊ lɔŋ] 美 [soʊ lɔŋ]
int. 再见;
拓展资料
双语例句
1. It's disgraceful that they have detained him for so long.
他们把他扣押了这么长时间，真不光彩。
2. Eleanor was annoyed at having had to wait so long for him.
埃莉诺为不得不等他这么长时间而感到很恼火。
3. It's very inconvenient to have to wait so long.
等这么久很麻烦。
4. "Be careful!" — "Sure thing, Dad. So long."
“要多加小心!”——“一定会的，爸爸。再见。”
5. Well, so long, pal, see you around.
再见了，朋友，咱们回见。
6. Jacob was silent so long that Livvy interposed.
雅各布沉默的时间太长了，莉薇只好插话了。
7. Sorry I took so long.
我耽误了这么长时间，真是对不起。
