[Question] Having hard time trying to create a chunk out to a function

[fatboyzz]

use anyhow::Result;
use itertools::Itertools;

fn main() -> Result<()> {
    let ns = vec![2, 2, 3, 3, 4, 4, 5, 5];

    let chunk = ns.iter().chunk_by(|n| *n % 2 == 0);
    // let chunk = chunked(ns.iter());

    let group = chunk.into_iter().take(2);
    for (even, ns) in group {
        println!("{} {:?}", even, ns.collect::<Vec<_>>());
    }
    Ok(())
}

// Don't know how to write the return type.
// Note that impl IntoIterator is not an option.
// the trait `IntoIterator` is implemented 
// - for `&itertools::ChunkBy<K, I, F>`
// - not `itertools::ChunkBy<K, I, F>`
//
// fn chunked(ns: impl Iterator<Item = i32>) -> impl IntoIterator {
//   ns.chunk_by(|n| *n % 2 == 0)
// }

• playground

[phimuemue]

Very ugly, but this may serve as a start:

use anyhow::Result;
use itertools::Itertools;

fn main() -> Result<()> {
    let ns = vec![2, 2, 3, 3, 4, 4, 5, 5];

    let chunk = ns.iter().chunk_by(|n| *n % 2 == 0);
    let chunk = chunked(ns.iter().copied());

    let group = chunk.into_iter().take(2);
    for (even, ns) in group {
        println!("{} {:?}", even, ns.collect::<Vec<_>>());
    }
    Ok(())
}

fn chunked(ns: impl Iterator<Item = i32>) ->
    itertools::ChunkBy<
        bool,
        impl Iterator<Item = i32>,
        impl FnMut(&i32)->bool
    >
{
   ns.chunk_by(|n| *n % 2 == 0)
}

[fatboyzz]

we can define chunked<I> where I is that Iterator. to not repeat the Iterator type.
also can't add F for the FnMut. Have to use the impl in return type.

[scottmcm]

I think we should close this; a question can go on URLO or something instead.

[fatboyzz]

The problem is not solved.

itertools::ChunkBy<
    bool,
    impl Iterator<Item = i32>,
    impl FnMut(&i32)->bool

Hand writing type like above is unrealistic for real iterators. Which may contains FlatMap then Map then ...
The core problem is ChunkBy is not IntoIterator. which limit its usage a lot.

[phimuemue]

Hand writing type like above is unrealistic for real iterators. Which may contains FlatMap then Map then ...
The core problem is ChunkBy is not IntoIterator. which limit its usage a lot.

I agree that it may be unhandy, but to me it seems it actually is IntoIterator IntoIterator if borrowed.

It may be worth posting the real use case either on URLO or here.

[fatboyzz]

the trait IntoIterator is implemented

• for &itertools::ChunkBy<K, I, F>
• not itertools::ChunkBy<K, I, F>

which is why i post this issue. I think is a api design issue.