Implemented [&]Cow<str> for SharedString

[npwoods]

Title is self-explanatory

[CLAassistant]

All committers have signed the CLA.

[ogoffart]

Thanks a lot for your PR.

I think it somehow makes sense.
Although this doesn't bring much value over shared_string.as_ref().into()

What is your use-case? Is the version that take a reference really necessary?

A small #[test] would be nice.

[ogoffart]

You don't need feature="std" if you use it from alloc:

Suggested change

	#[cfg(feature = "std")]
	use std::borrow::Cow;
	use alloc::borrow::Cow;

then the feature="std" is also not needed later.

[npwoods]

Learned something new. Thanks!

[ogoffart]

(Note that in the std library, From<Cow<str>> for String make sense since it can move the String when the Cow is owned. But this is unfortunately not possible for SharedString.)

[npwoods]

This change is clearly a very minor (borderline minuscule) improvement. Yes, it just saves an as_ref() but in a hypothetical future where there is a direct conversion from String to SharedString it would be beneficial (in a small way)

Strictly speaking, From<String> is not needed because as_str() could be use. (Yeah, of course, String is much more pervasively used than Cow<str>).

Thanks!

[ogoffart]

`One thing i was considering was to make SharedString able to hold &'static str depending on some bit tag.
eg: Improve SharedString to hold either of

• a pointer to a shared string like currently.
• a pointer to a static string and a length
• be inline (small string optimization)

In this case, it would be nice if one could convert from Cow<'static, str> without making an allocation.

In order to make it possible, would it make sense to restruct the implementation to 'static

Why do we need both Cow and &Cow ?

[npwoods]

In this case, it would be nice if one could convert from Cow<'static, str> without making an allocation

In that case you would not be able to use the changes I made, as (to my knowledge) there would not be a way to have both an implementation that converts from Cow<'static, str> and also a generic implementation for lifetimes over than 'static

Also, doesn't Slint rely SharedString being NUL-terminated?

Why do we need both Cow and &Cow?

We probably don't - I suppose I was just "aping" what I saw with [&]String