Implement Extend for Builder

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

The FromIterator trait is a standard trait in the ecosystem for building a collection from an iterator. Supporting it within the builders would allow writing code like (not tested)

let strings = ["1", "2", "3"];

let array = strings
    .iter()
    .map(|s| Some(s.parse()?))
    .collect::<Result<Int32Builder>>()
    .unwrap()
    .finish();

Describe the solution you'd like

Implement FromIterator for the Builder types. In most cases FromIterator is implemented for the corresponding Array type, and so it should largely just be a case of moving this logic into the builder and making the array implementation call it.

Describe alternatives you've considered

We could not do this

[heyrutvik]

@tustvold I'm trying to understand the ticket. If I'm not wrong, Extend will provide us extend method and then we can extend an existing builder using an iterator.

Example,

let ints = [1, 2, 3];
let mut builder = Int32Builder::new(0);
builder.extend(ints.into_iter());
let array = builder.finish();
assert_eq!(3, array.len());

given that we have impl Extend<i32> for Int32Builder implemented.

I'm confused because you mentioned Extend and not using any of its method in your example snippet. I believe collect is the main focus of your example which builds collection from an iterator. Could you please elaborate?

[tustvold]

Yes this is likely a brain fart on my part, the example should already be possible as we implement FromIterator. I think there is still value in implementing Extend, but perhaps less...

Edit: It was indeed a brain fart, I've updated the issue to be slightly more coherent. Let me know if you have any questions.

[heyrutvik]

Thanks @tustvold for the clarification. I started working on the ticket, and opened a draft PR #2038 for you to review to make sure whether I'm on the right direction or not. It adds FromIterator to BooleanBuilder and uses it in BooleanArray implementation. Once you confirm, I'll continue moving other existing FromIterator implementations. I moved all existing implementations to builder.