Tuple optional

[derekdreery]

This patch adds 2 features. Special care is needed with the Optional widget. While I'm sure it is very useful, I'm not sure I've implemented it correctly.

[maan2003]

Tuple lens looks good! For Optional, I recommend moving Runebender's Maybe to druid

[cmyr]

I have similar doubts about the correctness of my Maybe widget, but I've worked out at least some of the bugs, and it is certainly useful.

[derekdreery]

@cmyr could you comment on the difference between this Optional and runebender's Maybe? I didn't include a None option here, since you can get that functionality using Either, but maybe it makes more sense to include it. Also, how to handle events where the event should go to the widget (should_go_to_hidden, or something like that, and lifecycle events), but we don't have any data to send to the widget? I handled it by just sending the default value of the T of Option<T> to the some widget when the data was None, but this seems suboptimal.

EDIT wrote before I saw @cmyr 's comment 😛. I'd still be interested in your opinions on the questions.

[derekdreery]

And another question, if we have a widget for the None case, could we include a Null widget that lays itself out as bc.min() and does nothing else? It would go nicely with Maybe/Optional.

[cmyr]

in no order:

• there sort of is a Null widget, in the form of SizedBox::empty.
• I like letting there be a None option, in case you want a custom placeholder.
• I don't have any good answer about should_go_to_hidden. I think the solution I would advocate to not have the widget be hidden, but instead to create and destroy it as needed.

[derekdreery]

About the SizedBox::empty - it looks to be equivalent to a theoretical Null widget. My question is: how do we make this use of SizedBox discoverable?

[cmyr]

I'm open to suggestions!

[derekdreery]

@cmyr I've swapped out the Optional for runebender's Maybe, and added some intra-crate doc links.

[derekdreery]

Ready for review :)

[cmyr]

Do we need both Maybe and Optional? In my use, Maybe covers the optional category well enough.

[derekdreery]

Do we need both Maybe and Optional? In my use, Maybe covers the optional category well enough.

Oh I thought I had removed Optional. Will do.

[derekdreery]

Ready for review again.

[cmyr]

I won't make strong guarantees about covering all the corner cases in Maybe, but I haven't seen a crash in runebender in a while? 😬