looking-glass

---

constexpr utilities to determine the number of member fields in an aggregate struct, and produce a std::tuple with the same list of types.

Example usage

---

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

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

Requirements

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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 >= 4
• MSVC >= 19.14 (probably lower?)
• C++17

Build

---

The utility is header only, simply include "glass.hpp" to use.
There are a couple of customisation options for the header:

• Define GLASS_NAMESPACE if you want the utilities to live in a namespace other than glass.
• Disable the compile-time unit tests by defining GLASS_DISABLE_TESTS

Tests

---

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

TODO

---

• Support for anonymous unions and unnamed structs.
• Portable across GCC and Clang.
• Basic unit tests.
• Configurable namespace.
• Trace minimum MSVC version.
• Unit test tuple types with anonymous unions?
• Continuous integration.