I have a class, with a variadic template member function that attempts to expand a fold expression inside of a lambda. I think it is easier to explain with a minimal example.

struct GameState {

    using SystemFunc = std::function<void()>;

    std::vector<SystemFunc> m_systems;

    template <typename ComponentType>
    bool getComponent() const {
        return true;
    }
        
    template<typename... Components>
    void registerSystem() {
        m_systems.push_back([this]() {
            auto value = (getComponent<Components>() && ...);
            });
    }

};

This fails to compile with error C2662 ‘bool GameState::getComponent(void)’: cannot convert ‘this’ pointer from ‘GameState::registerSystem::<lambda_1>’ to ‘GameState &’ (on MSVC).

The error suggests this has something to do with const-correctness. I have tried every combination of ‘getComponent()’ being const/non-const and adding ‘mutable’ to the lambda. Making ‘registerSystem()’ const fails with a different error.

I have found a way to accomplish what I want using c++23’s deducing auto, however, I was curious why this doesn’t work.