以下代码按预期工作并获得结果：

ASM generation compiler returned: 0
Execution build compiler returned: 0
Program returned: 0
same
same
same

#include <iostream>
#include <type_traits>

struct Test {
    Test() {
        std::cout << "Test ctor\n";
    }
    int func() {
        return 1;
    }
};

int main() {
    if (std::is_same_v<decltype(std::add_rvalue_reference<Test>::type{}.func()),int>) {
        std::cout <<"same\n";
    } else {
        std::cout <<"different\n";
    }
    if (std::is_same_v<decltype(Test().func()),int>) {
        std::cout <<"same\n";
    } else {
        std::cout <<"different\n";
    }
    if (std::is_same_v<decltype(std::type_identity<Test>::type().func()),int>) {
        std::cout <<"same\n";
    } else {
        std::cout <<"different\n";
    }
}

但是，如果我将std::add_rvalue_reference<Test>::type{}替换为std::add_rvalue_reference<Test>::type()，则会生成以下编译错误：

<source>:14:33: error: reference to type 'Test' requires an initializer
    if (std::is_same_v<decltype(std::add_rvalue_reference<Test>::type().func()),int>) {
                                ^
1 error generated.
ASM generation compiler returned: 1
<source>:14:33: error: reference to type 'Test' requires an initializer
    if (std::is_same_v<decltype(std::add_rvalue_reference<Test>::type().func()),int>) {
                                ^
1 error generated.
Execution build compiler returned: 1

有谁知道是什么原因导致std::add_rvalue_reference<Test>::type()无法调用Test的构造函数，而Test()和std::type_identity<Test>::type()却很好？