Generate unique ID for subclasses

[opaque nebula]

So I have this struct ComponentBase:

struct ComponentBase {
  ComponentBase() = default;
};

Which is inherited by various other components. When you initialise an object, it may come with a couple of these subclassed components in a vector which each need to have a unique ID in the collection. I can't use typeid(obj) or typeid(obj).name() since pybind11 doesn't work with the first one and the strings are name scrambled with the second.

Its also pretty difficult to use a virtual function to do get_type() for the component since I have methods like this:

  template <typename T>
  inline auto get_component(const GameObjectID game_object_id) const -> std::shared_ptr<T> {
    return std::static_pointer_cast<T>(get_component(game_object_id, GET_COMPONENT_TYPE_HERE));
  }

  [[nodiscard]] auto get_component(GameObjectID game_object_id, TODO component_type) const -> std::shared_ptr<ComponentBase>;

Which can't be passed an instance of the component since I'm trying to get that component. What would be the best way to solve this?

[wooden canopy]

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[knotty badge]

why does your code require a unique id for each instance

[opaque nebula]

Its not for each instance, its for each type of component so a unique ID for each class

[knotty badge]

so why cant you use a virtual halper func get_type

that returns some enum value

[opaque nebula]

  template <typename T>
  inline auto get_component(const GameObjectID game_object_id) const -> std::shared_ptr<T> {
    return std::static_pointer_cast<T>(get_component(game_object_id, GET_COMPONENT_TYPE_HERE));
  }

How would I get the type here? It would need an instance

[knotty badge]

here you have an instance of std::shared_ptr<T>, from here you can call the virtual functions that T has

that's how

[opaque nebula]

I'm calling get_component to get the component and I cast it to T. get_component expects the component type

[knotty badge]

so based on you passing the T explicitly, you know what T is, you can use a static function in T instead of a virtual one

{
  static CompType getType()
  {
    return CompType::MAGIC_COMPONENT;
  }
}

?

[opaque nebula]

can that be overriden in the subclasses? for some reason when i tried earlier, it didn't work

[knotty badge]

yes

you can redefine any static function in any class, inheritance is irrelevant

[hard flame]

@opaque nebula you could use std::type_index

There's also some tricks to get a unique random I'd for each class

[hard flame]

I really dislike that because you need to manually maintain it

[opaque nebula]

I can't use std::type_index. I have some pybind11 bindings for this class and it can't convert std::type_index

[hard flame]

You could always get the hash from the type_index and hope for the best

[opaque nebula]

For get_component, its definition would be:

auto Registry::get_component(const GameObjectID game_object_id, const std::type_index &component_type);

And pybind11 can't convert std::type_index to Python

It would make this easier, but whatever. Static methods seem to work now, idk why they wern't working earlier though

[hard flame]

Do you need to be able to get that Id from the python side?

Or are you getting that Id from the CPP side and passing it to python?

[opaque nebula]

Its used on the C++ side, but I'm not sure how I would pass in a value from python which will let me get that component out

So you would think that passing type(obj) from python would work, but it can't be converted to std::type_index which is kinda annoying so I'm having to try this other approach

[hard flame]

https://godbolt.org/z/es3j9z5Yb

[opaque nebula]

?

[hard flame]

it gives you an unique ID for each type

[opaque nebula]

but would it allow for a python interface

[hard flame]

if you get the ID from the cpp side you should be able to pass it no problem

[opaque nebula]

its about passing a value from the python side

[hard flame]

but where are you creating it from?

[opaque nebula]

i was just using typeid() in the c++ code

[hard flame]

alright so what's the problem?

[opaque nebula]

how would i pass a value from python to c++ which is used to find a component stored

[hard flame]

do you pass the value from cpp to python and then back to cpp?

[opaque nebula]

i pass the type i want from python to cpp and cpp should pass the component back

[hard flame]

where/how do you get the type on the python side?

[opaque nebula]

thats what im trying to figure out, how would i know what to pass so c++ can read it? ive been using strings and since i know what their value is, its easy to pass the string to c++ and get the component

[signal saffron]

you will need some kind of "registry" on the C++ side that knows all the possible IDs anyway,
and a way to then instantiate the correct type of thing

[opaque nebula]

i may just stay with the static method idea for now. i can always change it later on