docs for extend_from_slice say extend isnt specialized for slice yet

[bjorn3]

Noticed an error in the docs of Vec::extend_from_slice:

Note that this function is same as extend except that it is specialized to work with slices instead. If and when Rust gets specialization this function will likely be deprecated (but still available).

extend is already specialized for slices

[frewsxcv]

@rust-lang/libs Are there plans to deprecate extend_from_slice in favor of extend, or can we just remove this comment altogether?

[SimonSapin]

If I remember correctly, the plan is to start "publicly" taking advantage of specialization in the standard library (even if indirectly, such as by recommending extend over extend_from_slice) after specialization is stable in the language, because of uncertainty around what eventually will or will not be allowed by specialization.

[alexcrichton]

Yes until specialization is stable we do not want to deprecate this method.

[steveklabnik]

Seems like this is blocked on specialization, so tagging with low priority.

[briansmith]

On the other hand, the documentation for Extend<&'a T> says that it is specialized for slice iterators, and it is pretty important that it is; otherwise we'd need extend_from_slice to be generalized into a trait.

[Icelk]

Any news on this? Should I make a pull request depreciating the method or tweak the docs?

[thomcc]

Seems like it's still blocked on specialization stabilizing...

[Icelk]

But I can’t help but notice the function (in the alloc source) turns the slice to an iterator an passes it to extend()
extend_from_slice is then an middlehand

[thomcc]

Yes, that's already been discussed.

[Icelk]

So the function exists only if specialisation would disappear for slice iterators in the future?
Are there any updates on specialisation in the last two years?

[thomcc]

Yes: #31844

It's also possible it will go the same route as const generics with a min_specialization (which already exists) stabilizing first. But it might not too, and might need to wait for Chalk to be integrated into the compiler more fully.

[Icelk]

Okay.
The function docs suggest it’s not specialised, as the issue author points out, but seeing as it turns it into an iterator, the docs are miss-leading. Should we change them?