A small summary for idiomatic Rust

I got myself into simple problem: to split string into pieces by space. During this …ehem… problem I found I need to filter empty splits if there is more than one space in row.

My intial code was:

foo.split(" ").filter(|e| e.len() > 0).collect()

I asked on Reddit if it can be shorter, and after few discussion twists of different hospitality, there were few important takeaways I want to summarize.

Split

There are few helpful functions of splitting, and most of them are not in String, but in str .

• split (the one I started with)
• split_whitespace (which honor all unicode spaces and consumes multiple spaces without producing empty &str).
• split_ascii_whitespace (which honor ascii-only-whitespaces). My problem is sovled by it.

Also, it’s better to split with ' ', and not with " " (split by char, not by &str), which is subtle, but important for performance.

(But discussion continued!)

Filter

Th expression |e| e.len() > 0 is ugly. But of course there is a better option: |e| !e.is_empty() .

Also, flatten (which is not applicable in my case) is skipping empty Option/Result.

Truthy

One thing I said in discussion is comparison with truthy Python. I got reprimanded for that and I listened for arguments about semi-automatic casting to booleans. It’s important.

Missing things in Rust

The discussion also leaded to some ideas:

• Can we have skip_default iterator which skip default value? Most types has Default trait, so it’s easy to implement. Default+PartEq …
• .len and .is_empty , basically, sounds like a part of a trait. But there is none. Container may be a good trait… And then you can have .skip_empty implemented for Item=T: Container .

It is not there, but worth think and reason about. May be they should be? Or may be they are redundant.

Conclusion

There is no specific conclusion, but attention to small things let intuition to grow. I got slightly more familiar with iterators over str (and that they are in str, not in String is important!), and got better view on types.