一元负重载：成员还是非成员？
鉴于前缀一元运算符可以“由不带参数的非静态成员函数或带一个参数的非成员函数实现”(§13.5.1[over.unary]/1)，除了适用于任何成员/非成员函数选择的通常封装/代码重用设计原理之外，还有什么区别吗？
对于二元运算符，存在语义差异，因为非-成员允许对其左侧操作数进行隐式转换。一元运算符似乎没有类似的东西，但标准将 std::complex 的一元否定运算符定义为非成员（§26.4.6[complex.ops] )，而 std::valarray 和 std::duration 的一元否定运算符是成员（§26.6.2.6[valarray.unary]，§20.11.5.3[time.duration.arithmetic]）。有细微差别吗？
Given that prefix unary operators can be "implemented by a non-static member function with no parameters or a non-member function with one parameter" (§13.5.1[over.unary]/1), is there a difference besides the usual encapsulation/code reuse design rationales that apply to any member/non-member function choices?
For binary operators, there's a semantic difference because non-members allow implicit conversions of their left-hand operands. There doesn't seem to be anything like that for the unary operators, yet the standard defines std::complex's unary negation operator as a non-member (§26.4.6[complex.ops]), while std::valarray's and std::duration's unary negation operators are members (§26.6.2.6[valarray.unary], §20.11.5.3[time.duration.arithmetic]). Is there a nuance?
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据我所知，与决定非运算符函数应该是成员还是非成员相比没有区别。显然，如果可能的话，更喜欢非成员、非朋友（就像标准算法一样）。
As far as I'm aware there are no differences as compared to deciding if a non-operator function should be member or non-member. Obviously prefer non-member, non-friend when possible (like the standard algorithms).
尽可能使用会员更有意义，因为您不必与朋友一起疯狂。但除此之外，这只是代码风格的决定。
Using members when possible makes more sense, since you don't have to go crazy with friends. But otherwise, it is just a code style decision.