第六十一条 承运人将货物运输或者部分运输委托给实际承运人履行的，承运人仍然应当依照本章规定对全部运输负责。对实际承运人承担的运输，承运人应当对实际承运人的行为或者实际承运人的受雇人、代理人在受雇或者受委托的范围内的行为负责。
If we don’t do this with lists, if we don’t make += do the in place assignment, if we don’t leave it open for types to do their own thing, depending on the circumstances, then there’s no value in += in the first place, because it’s just syntactic sugar for +.
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