将括号内的初始值设定项列表作为结构返回

下面给出用 g++ -c test.cpp 或 g++ -std=c++17 -c test.cpp

#include <cstddef>

struct sd_bus_vtable {
        union {
                struct {
                        size_t element_size;
                } start;
                struct {
                        const char *member;
                        const char *signature;
                } signal;
        } x;
};

sd_bus_vtable get()
{
    return {
        .x = {
            .signal = {
                .member = "",
                .signature= "",
            }
        }
    };
}

它在GCC 9.2.0和clang 5/6上编译良好,但在8.3.0或7.4.0上编译失败,错误消息如下:

test.cpp:25:5: error: could not convert ‘{{{"", ""}}}’ from ‘<brace-enclosed initializer list>’ to ‘sd_bus_vtable’
     };

为了解决这个问题,函数 get() 可以按以下方式更改,但看起来不太干净。。。

sd_bus_vtable get()
{
    struct sd_bus_vtable t = {
        .x = {
            .signal = {
                .member = "",
                .signature= "",
            }
        }
    };
    return t;
}

问题是,上述代码是否有效?如果是,它是否会触发GCC中修复的GCC9中的某些错误?