在 C++ 标准中，下面的代码片段中不允许使用 `a = b + {1, 2}`？

Question

标准中的哪个地方 a = b + {1, 2} 下面是不允许的？

class complex {
    double re, im;
public:
    complex(double r, double i) : re{ r }, im{ i } {}
    complex& operator+=(const complex& other) { re += other.re; im += other.im; return *this; }
};

inline complex operator+(complex lhs, const complex& rhs)
{
    lhs += rhs;
    return lhs;
}

int main()
{
    complex a{ 1, 1 };
    complex b{ 2, -3 };
    a += {1, 3};          // Ok
    a = b + {1, 2};       // doesn't compile
}

Answer 1

由于未在 N3797 §8.5.4 [dcl.init.list]/1（强调我的）中列出而被禁止：

Note: List-initialization can be used

as the initializer in a variable definition (8.5)

as the initializer in a new expression (5.3.4)

in a return statement (6.6.3)

as a for-range-initializer (6.5)

as a function argument (5.2.2)

as a subscript (5.2.1)

as an argument to a constructor invocation (8.5, 5.2.3)

as an initializer for a non-static data member (9.2)

in a mem-initializer (12.6.2)

on the right-hand side of an assignment (5.17)

强调的要点与您的 a += {1, 3}; 相对应。没有符合加法论点的点。

在 C++ 标准中，下面的代码片段中不允许使用 `a = b + {1, 2}`？

Where in the C++ Standard is `a = b + {1, 2}` disallowed in the snippet below?

c++

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