CODEWITHSUNDEEP
rustiterator
rump roast
rump roast

Reputation: 814

How to apply a series of iterators to data?

I'm tinkering with Rust by building some basic genetics functionality, e.g. read a file with a DNA sequence, transcribe it to RNA, translate it to an amino acid sequence, etc.

I'd like each of these transformations to accept and return iterators. That way I can string them together (like dna.transcribe().traslate()...) and only collect when necessary, so the compiler can optimize the entire chain of transormations. I'm a data scientist coming from Scala/Spark, so this pattern makes a lot of sense, but I'm not sure how to implement it Rust.

I've read this article about returning iterators but the final solution seems to be to use trait objects (with possibly large performance impact), or to hand roll iterators with associated structs (which allows me to return an iterator, yes, but I don't see how it would allow me to write a transformation that also accepts an iterator).

Any general architectural advice here?

(FYI, my code so far is available here, but I feel like I'm not using Rust idiomatically because a. still can't quite get it to compile b. this pattern of lazily chaining operations has led to unexpectedly complex and messy code that only works on Rust nightly.)

Upvotes: 0

Views: 170

Answers (1)

Optimistic Peach
Optimistic Peach

Reputation: 4318

Iterator adaptors are meant to do operations which can't easily be expressed otherwise. Your two examples, .translate(), and .transcribe(), given your explanation of them, could be simplified to the following:

dna
    .map(|x| x.translate())
    .map(|x| x.transcribe())

// or

dna
    .map(|x| x.translate().transcribe())

However, if you are intent on designing your own iterator, the following should work:

struct Transcriber<I: Iterator<Item = Dna>> {
    inner: I
}

impl<I: Iterator<Item = Dna>> Iterator for Transcriber<I> {
    type Item = TranscribedDna;
    fn next(&mut self) -> Option<Self::Item> {
        self.next().map(|x| x.transcribe())
    }
}

// Extension trait to add the `.transcribe` method to existing iterators
trait TranscribeIteratorExt: Iterator<Item = Dna> {
    fn transcribe(self) -> Transcriber<Self>;
}

impl<I: Iterator<Item = Dna>> TranscriberIteratorExt for I {
    fn transcribe(self) -> Transcriber<Self> {
        Transcriber { inner: self }
    }
}

Then you can use

dna
    .transcribe() // yields TranscribedDna

Upvotes: 2

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