pure-reflection.md

Pure Reflection

Glaze supports pure reflection for aggregate initializable structs in Clang, MSVC, and GCC.

Aggregate initializable means:

• no user-declared constructors
• no user-declared or inherited constructors
• no private or protected direct non-static data members
• no virtual base classes

There's no need to write any glz::meta structures or use any macros. The reflection is hidden from the user and computed at compile time.

• You can still write a glz::meta to customize your serialization, which will override the default reflection.

CUSTOMIZATION NOTE:

When writing custom serializers specializing to_json or from_json, your concepts for custom types might not take precedence over the reflection engine (when you haven't written a glz::meta for your type). The reflection engine tries to discern that no specialization occurs for your type, but this is not always possible.

To solve this problem, you can add static constexpr auto glaze_reflect = false; to your class. Or, you can add a glz::meta for your type.

Mixing glz::meta reflection with pure-reflected structs

If you have an struct with constructors you may need to use glz::meta to define the reflection. But, now your type might break the counting of the numbers of members when included in another struct.

To fix this, add a constructor for your struct to enable the proper counting: my_struct(glz::make_reflectable) {}

Example:

struct V2
{
   float x{};
   float y{};

   V2(glz::make_reflectable) {}
   V2() = default;

   V2(V2&&) = default;
   V2(const float* arr) : x(arr[0]), y(arr[1]) {}
};

template <>
struct glz::meta<V2>
{
   static constexpr auto value = object(&V2::x, &V2::y);
};

struct V2Wrapper
{
   V2 x{}; // reflection wouldn't work except for adding `V2(glz::make_reflectable) {}`
};