add MutableVector::mut_split(self, pred) -> DoubleEndedIterator<&mut [T]>

[TeXitoi]

I've renamed MutableVector::mut_split(at) to MutableVector::mut_split_at(at) to be coherent with ImmutableVector. As specified in the commit log, The size_hint method is not optimal because of #9629.

[TeXitoi]

Sorry, I rebased before seeing @cmr r+

[TeXitoi]

The tests are buggy, they don't compile. I'll correct that when I can.

[alexcrichton]

I would expect mut_split to take an integer and this function to rather be named something like mut_split_when, but this is also going a little bit into the territory of me questioning whether it should be included in libstd.

Is there a common use case for an iterator like this?

[alexcrichton]

I was also a little confused when reading the documentation about whether the element the predicate is run on is included in the slice of the iterator or not (I think this needs some more explicit working in the function documentation).

[Kimundi]

@alexcrichton The split (and with this PR mut_split) iterators on vectors work like this because they copy the API on strings: "a b c d".split(char::is_whitespace) for example - Granted, it might be more obvious there.

However, given the fact that there are multiple ways you could split a slice: At an index, at places where a predicate holds, at chars for strings etc, it is indeed uncertain how the API should look, and what name to give the functions - that seems like a broader issue though. Short term, making split and mut_split consistent by renaming either seems to be higher priority to me.

As an aside, I'm planning to improve and unify the string API for finding a contained pattern in general, and would then likely try to port whatever I come up with to vectors.

[TeXitoi]

for mut_split -> mut_split_when (or mut_split_with?), I can do the change, but I'll have to change ImmutableVector::split(). But as @Kimundi said, maybe it's better to let it like that for now.

For the documentation, it's the same as ImmutableVector::split(). I can update the two.

I needed this iterator during my shootout-reverse-complement.rs rewrite, that is basically reversing a &mut [u8] sepparated by >. Maybe it can be useful to modify binary stream (as putting uppercase some fields of csv file).

[TeXitoi]

Tests fixed (pass here) and split doc clarified.

[TeXitoi]

@alexcrichton Remarks? OK?

[alexcrichton]

looks good to me, could you squash the last two commits together?

[TeXitoi]

@alexcrichton squashed.