See the new static-reflection repo that houses this utility nitronoid/looking-glass.

A constexpr utility to determine the number of member fields in an aggregate struct.

// Struct with three member variables
struct S
{
    char a, b, c;
};

// Check that S has three members at compile time
static_assert(stdex::member_count<S> == 3, "S does not have 3 members.");

This lib requires GCC version 9 or above due to a bug fix provided for uniform aggregate initialisation of unions. I haven't traced back the minimum MSVC version yet, but it does work with v19.14 and above.

• GCC > 9.0.0
• Clang > 3.5.0
• MSVC > 19.14 (probably lower?)
• C++14

The utility is header only, simply include "member_count.hpp" to use (or "member_count_cpp20.hpp" to use concepts).

The unit tests have been added as static_asserts (because why not?) and are included at the end of the main header so they are always checked. A dummy translation unit has been provided for easy of checking the compilation:

$(CXX) test/test.cpp

• Support for anonymous unions and unnamed structs.
• Portable across GCC and Clang.
• Basic unit tests.
• Trace minimum MSVC version.
• More unit tests.
• Configurable namespace.
• Continuous integration.