[SOLVED] Is using-declaration with an anonymous enum valid in modern C++

Is using-declaration with an anonymous enum valid in modern C++

I know that the following typedef-based code works fine and is widely used:

class Example {
public:
    typedef enum {
        eOrdered,
        eRandom
    } tePoolOrder;
};

Clang-tidy has now automatically modernized it as follows.

class Example {
public:
    using tePoolOrder = enum {
        eOrdered,
        eRandom
    };
};

This compiles without issues in my C++17-setup (Clang/GCC), but I’m unsure whether this syntax is standard-compliant or if it relies on compiler-specific behavior.

I understand that using typically aliases named types, so is this usage with an anonymous enum supported by the C++ standard? If not, should I switch to a named enum for portability? What would be the correct modern C++ approach to achieve this?

Any clarification would be appreciated!
Try it out here: https://onlinegdb.com/3FuchkJ5Y

Solution

Simplified, the syntax of using for type-aliases is

using alias = type;

For your case the alias is tePoolOrder and the type is enum { ... }.

This is perfectly valid.

This is very similar to typedef, which has the syntax (again simplified):

typedef type alias;

Hopefully this helps to see that the type is the same, and that enum { ... } is a type and not an anonymous enumeration.