Cannot move or copy instance of a class exposing Slot without breaking callback

[michaelcowan]

The intended use of ass for class decoupling will not invoke the callback of the expected instance when copied or moved.

e.g.

class Popup {
public:
    Slot<> show = Slot<>(this, &Popup::render);
private:
    void render() {
        Popup * pointer = this;
    }
};

Popup popup;
Signal<> signal;
signal.connect(popup.show);

Popup movedPopup = std::move(popup);

signal.emit();

Here, calling emit() will trigger the instance of Slot belonging to movedPopup, which is as expected. However the value of this in the callback method render() will be that of popup.

This is because the callback function in Slot (which contains the this value of popup) was moved into the Slot instance in movedPopup - this is as intended for Slot copy/move semantics, but when that function contains a pointer to this we get unexpected results, like this.

[michaelcowan]

Just for context, pushing this onto the client could look something like this

class Popup {
public:
    Slot<> show = Slot<>(buildShowCallback());

    Popup() = default;

    Popup(Popup &&other) noexcept {
        this->show = std::move(other.show);
        this->show.setCallback(buildShowCallback());
    }
private:
    std::function<void()> buildShowCallback() {
        return [this]() { render(); };
    }
    void render() {
        Popup * pointer = this;
    }
};

Popup popup;
Signal<> signal;
signal.connect(popup.show);

Popup movedPopup = std::move(popup);

signal.emit();

😞