Remove one shot commands.

[luleyleo]

Fourth part of #908 .

I gave the suggestion by @cmyr a try and replaced one shot commands with a SingleUse wrapper type and it seems to work really well.

To summarize the change:

ctx.submit_command(
    Command::one_shot(commands::NEW_WINDOW, desc),
    Target::Global,
);

let desc = cmd.take_object::<WindowDesc<T>>().unwrap();

is now

ctx.submit_command(
    Command::new(commands::NEW_WINDOW, SingleUse::new(desc)),
    Target::Global,
);

let desc = cmd.get_object::<SingleUse<WindowDesc<T>>>().unwrap().take().unwrap();

which can easily be utilized by typed selectors.

[xStrom]

Looks decent overall.

[cmyr]

Cool yea I think this is an improvement. A few comments inline, but looks good!

[cmyr]

this type isn's actually exposed anywhere, so I don't think external crates can access it?

Also I would expect this to need to be in an Arc, since the Event itself still needs to be cloneable?

[luleyleo]

Good catch, I've reexported it from lib now.

Not sure what you mean regarding the Arc. When using SingleUse the payload will be stored the exact same way as it used to with Arg::OneShot, minus the Box<Any> wrapper as it is now directly stored as Arc<Any>.

[cmyr]

ah okay I missed that the Arc has moved into the signature of the object field on Command.

[cmyr]

huh I think I lost a comment here?? anyway, to try again:

Doc comments are kind of like git commit messages; you want the first paragraph to be a short general overview that doesn't need a lot of context, and then a blank line, and then a more detailed explanation.

This is because the first paragraph is displayed beside the type name in the module or crate level docs.

For this type, for instance, I would try a first paragraph of something to the effect of,

"A wrapper type for Command arguments that should only be used once."

[luleyleo]

Thanks, I should have actually built the docs 😅

I've added the suggested head paragraph, and while I was at it also an example how to make use of SingleUse.

[cmyr]

One little non-blocker, thanks for this!

[xStrom]

Looks good!