Add `Option<Res>::cloned`

[evaogbe]

What problem does this solve or what need does it fill?

Res does not implement Clone, but instead has a custom clone method. This does not play well when using an Option<Res> that you need to clone since Option::cloned requires the inner type to implement Clone.

What solution would you like?

It would be nice to have an extension to Option<Res> that creates a custom cloned method that calls the custom Res::clone method. Then I could do something like this:

let slot_transfer_data = mouse_data
        .cloned()
        .filter(|m| m.location == MouseLocation::Slot)
        .and_then(|m| m.inventory_index);
let map_transfer_data = mouse_data
        .cloned()
        .filter(|m| m.location == MouseLocation::Map)
        .and_then(|m| camera.viewport_to_world_2d(camera_transform, m.position));

What alternative(s) have you considered?

Right now my code looks like this:

let (slot_transfer_data, map_transfer_data) = if let Some(mouse_data) = mouse_data {
        let slot_transfer_data = if mouse_data.location == MouseLocation::Slot {
            mouse_data
                .inventory_index
                .zip(dragged_item.data)
                .filter(|(dest_index, (dragged_index, _))| dest_index != dragged_index)
        } else {
            None
        };
let map_transfer_data = if mouse_data.location == MouseLocation::Map {
            camera
                .viewport_to_world_2d(camera_transform, mouse_data.position)
                .zip(dragged_item.data)
        } else {
            None
        };
        (slot_transfer_data, map_transfer_data)
    } else {
        (None, None)
    };

IMO it's pretty messy. It's possible there's a simpler workaround already existing. I am new to Rust, so this is the best I've got.

Additional context

I think I know just enough Rust to be able to contribute this if y'all think it's worth it. Also this change doesn't appear to be breaking, so that's nice.

[mockersf]

#4109 for context on why the trait is not implemented

[TheBlek]

For this particular use case you could probably write something like this:

let (slot_transfor_data, map_transfer_data) = match mouse_data {
    Some(mouse_data) if mouse_data.location == MouseLocation::Map => {
        (Some(mouse_data.data), None)
    },
    Some(mouse_data) if mouse_data.location == MouseLocation::Slot => {
        (None, Some(mouse_data.data))
    },
    _ => (None, None)
};

Also, as far as I know this would get rid of the clone in question entirely.

[evaogbe]

Thanks for the tip! I guess the question remains whether there are other usecases that can't be solved in the same way