send_future_batch requires a Vec, doesn't accept an Option

[lilyball]

Problem
batch_callback() works with any result type that implements SendAsMessage, which basically means either Option or Vec. But send_future_batch() requires Vec. This feels like an unnecessary limitation, it should be able to use SendAsMessage as well so that way I can have a future that optionally sends a message.

Arguably send_message_batch() could take SendAsMessage as well for consistency, though it's less important there as I can simply choose to not send a message if I have None. If you add a batch_callback_future() (which seems like a missing hole right now) then that too should use SendAsMessage.

Environment:

• Yew version: 0.19.3

Questionnaire

• I'm interested in fixing this myself but don't know where to start
• I would like to fix and I have a solution
• I don't have time to fix this right now, but maybe later

[WorldSEnder]

To explain a bit of the reasoning, send_message* are internally used as the low-level primitive that the SendAsMessage impls use.

If you have maybe_msg: Option<Message> you should be able to maybe_msg.send(&link) to achieve the same effect as explicitly pattern matching on the option and doing link.send_message(..) (with use yew::html::SendAsMessage somewhere).

I agree that batch_callback_future is a bit of a hole right now, but moreover, Callback is perhaps missing a way to construct it from an async function, without explicitly having to call spawn_local. Then you could also easily construct that callback yourself.