Add Iterator::into_vec()

[HyeonuPark]

Though we have nice Iterator::collect(), the most common use cases of this method as I've seen are my_iter.collect::Vec<_>(), which is a bit complicated to type. So it would be worth to add this simple shortcut method for it.

#[inline]
fn into_vec(self) -> Vec<Self::Item> {
    self.collect::<Vec<_>>()
}

[leonardo-m]

Is the "to_vec" name better (and shorter)?

[Ixrec]

The other container I very frequently see collect targeting is String, so we may also want an into_string or to_string method.

Whether or not we do that, I'd prefer the into names, since into_* implies a conversion that consumes/destroys/moves the original value (which iiuc is exactly what collect does), while to_* implies some amount of copying is involved so that the original value remains intact. In particular, slices/strs already have to_vec/string and into_vec/string methods with exactly these semantics.

[F001]

I think this can be done in your own crate. The motivation of adding it to std is not strong enough.

[leonardo-m]

If your program is short, doing this in your own crate is overkill.

I think it's a good idea to have a standard method like this because .collect::<Vec<_>>() is long, very common in iterators-based code, not handy to write, quite visually noisy, not easy to discover and remember for newbies.

.into_vec() is visually only one (or two) chunks, compared to .collect::<Vec<_>>(). In D language you can convert a range to an array with just ".array".

Sometimes you can replace .collect::<Vec<_>>() with .collect() and assign the result to a variable that's typed with :Vec<_>, but in longer iterators chains this can't be done.

The need for conversion to a vector is very common (but once the impl trait feature becomes stable, more functions will return an iterator, so some usages of .collect::<Vec<_>>() will be removed).

The itertools crate has this function, named ".collect_vec()":

https://docs.rs/itertools/0.5.9/itertools/trait.Itertools.html#method.collect_vec

[bluss]

collect_vec seems to be one of the more popular methods in itertools, if popularity feelings say anything. Best methods from itertools should move into libstd somehow.

Note that Iterator can't include a method called collect_vec or to_vec, because Iterator is in libcore.

[bluss]

Wishes for new features (things that are not defects) are filed in the rust-lang/rfcs repo.

I think the most successful way to get a new feature into Rust would be something like:

1. Sound it out in the https://internals.rust-lang.org/ forum. They will know if a PR or RFC is the best way to go. For RFCs I really recommend posting them as Pre-RFC threads on internals before filing the real thing.
2. File appropriate PR or RFC

I'll close this issue with that information.

[HyeonuPark]

This topic is moved to this thread. Thank you for letting me know the right place to post it.