Making an own-able struct of Cows

[chrome tapir]

Behold the following: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1ca7f62bcf7540e35171195d5751833a

It's a struct full of cows for str.
I would like to be able to use block_tag.to_owned() to get an owned version of the BlockTag, which is just a BlockTag<'static>.
You can see in this playground that it gives me a lifetime error though, which confuses me since the owned type shouldn't be dependent on the lifetime of the borrowed type, right?

[rare oyster]

the owned type shouldn't be dependent on the lifetime of the borrowed type, right?
It is, in the case of Cow.

The reason for that is that a Cow is not very useful past the lifetime where it would be valid if it was borrowed

To elaborate, if you have a Cow<'a, str> and you keep it around for longer than 'a (you can't actually do this, pretend you could), then you can't access it anymore unless you're certain it's owned: if it was borrowed, you'd be accessing a dangling reference

But if you're certain it's owned, why do you even have a Cow

Just have a String, or in general the owned type

Now, as you noticed there is a valid reason to have a Cow where you're certain it's owned, but .to_owned() on Cow doesn't actually "decouple" the lifetime.

(that's because Cow doesn't implement ToOwned, it's just Clone. You're calling the default implementation of ToOwned for Clone types)

To decouple it by hand, you can use Cow::Owned(cow.into_owned()), which will convert to owned (or extract the existing owned contents), then put them in a new cow, which can have a different lifetime

[chrome tapir]

Ohhh now that makes sense.

Thanks. I had a feeling I was missing something simple.

That explains why the owned type can't just be a 'static version of the original type.