Anonymous struct as a return type

问题:

The following code compiles fine with vc++ 19.00.23506 (flags: /Wall /WX /Za) and with vc++ 19.10.25109.0 (flags: /Wall /WX /Za /permissive-, this can be checked at http://webcompiler.cloudapp.net), but doesn't compile with clang 3.8.0 and g++ 6.3.0 (flags: -std=c++11 -Wall -Wextra -Werror -pedantic-errors). Is it a bug in vc++ and does the standard prohibit such constructions?

struct
{
}
foo()
{
    return {};
}

int main()
{
}

回答1:

MSVC appears wrong:

[dcl.fct]/9 Types shall not be defined in return or parameter types...

回答2:

You can return anonymous type, but you have to define it inside the function:

auto foo()
{
    struct {} s;
    return s;
}