子结构体的大括号初始化

Question

有没有办法通过包含基本结构成员变量来使用大括号初始化子结构。我正在尝试以下操作，但无法编译（使用 VS 和 C++ 20）。 我不想创建构造函数，而是想使用单行构造。

struct Base
{
    int n;
};

struct Derived : Base
{
    std::string s;
}

static const Derived d1{ .s = "Hi", { .n = 1 } }; //fails to compile
static const Derived d2{ 1, { "Hi" } };           //fails to compile
static const Derived d3{ 1, "Hi" };               //fails to compile
static const Derived d4(1, "Hi");                 //fails to compile

编辑：

d4, d3

实际上编译得很好。

Answer 1

这对我有用，https://godbolt.org/z/oYWYr5Gc7：

#include <string>

struct Base {
  int n;
};

struct Derived : Base {
  std::string s;
};

// Designated-initializers must be in the order of the member declarations.
// Base data members precede Derived data members.
static const Derived d1 = {{.n = 1}, .s = "Hi"};

static const Derived d2{1, {"Hi"}};
static const Derived d3{ 1, "Hi" };

// It does not work because Derived does not have the constructor.
// static const Derived d4(1, "Hi");