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Sort out join-semantics for archetypes with multiple required components #2750

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jleibs opened this issue Jul 18, 2023 · 0 comments · Fixed by #5573
Closed

Sort out join-semantics for archetypes with multiple required components #2750

jleibs opened this issue Jul 18, 2023 · 0 comments · Fixed by #5573
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@teh-cmc
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codegen/idl enhancement New feature or request

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jleibs commented Jul 18, 2023

I've come into a few places where I'm effectively treating the first required component as what we used to call the primary component.

The only really important thing about the primary component is that is defines the set of instance-keys... but since a required component must be defined for every instance-key, we have two choices:

  • Make it an error to use component-level APIs to log required components with different key values.
  • When iterating, take the itersection of instance-keys for all required components.
@jleibs jleibs added enhancement New feature or request codegen/idl labels Jul 18, 2023
@teh-cmc teh-cmc self-assigned this Mar 15, 2024
@teh-cmc teh-cmc mentioned this issue Mar 19, 2024
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@teh-cmc teh-cmc linked a pull request Mar 19, 2024 that will close this issue
New data APIs 0: ClampedZip iterator machinery #5573
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teh-cmc added a commit that referenced this issue Apr 8, 2024
@teh-cmc
New data APIs 0: ClampedZip iterator machinery (#5573)
e158114 
This introduces a new temporary `re_query2` crate, which won't ever be
published.
It will replace the existing `re_query` crate once all the necessary
features have been backported.

As of this PR, this crate only contains the `ClampedZip` iterator
machinery, which is code generated for all the different arities.

Since I'm very, _very tired_ of the awful DX of macros, I implemented a
very low-tech code generator in the crate itself
(`src/bin/clamped_zip.rs`) that just spews the generated code on stdout.
That seems like the right complexity-to-maintenance tradeoff,
considering that iterator combinators don't really ever change.

`ClampedZip` naturally works with more than one required component,
finally!

- Fixes #4742
- Fixes #2750

Here's an example of one of these combinators:
```rust
/// Returns a new [`ClampedZip1x2`] iterator.
///
/// The number of elements in a clamped zip iterator corresponds to the number of elements in the
/// shortest of its required iterators (`r0`).
///
/// Optional iterators (`o0`, `o1`) will repeat their latest values if they happen to be to short
/// to be zipped with the shortest of the required iterators.
///
/// If an optional iterator is not only too short but actually empty, its associated default function
/// (`o0_default_fn`, `o1_default_fn`) will be executed and the resulting value repeated as necessary.
pub fn clamped_zip_1x2<R0, O0, O1, D0, D1>(
    r0: R0,
    o0: O0,
    o0_default_fn: D0,
    o1: O1,
    o1_default_fn: D1,
) -> ClampedZip1x2<R0::IntoIter, O0::IntoIter, O1::IntoIter, D0, D1>
where
    R0: IntoIterator,
    O0: IntoIterator,
    O0::Item: Clone,
    O1: IntoIterator,
    O1::Item: Clone,
    D0: Fn() -> O0::Item,
    D1: Fn() -> O1::Item,
{
    ClampedZip1x2 {
        r0: r0.into_iter(),
        o0: o0.into_iter(),
        o1: o1.into_iter(),
        o0_default_fn,
        o1_default_fn,
        o0_latest_value: None,
        o1_latest_value: None,
    }
}

/// Implements a clamped zip iterator combinator with 2 required iterators and 2 optional
/// iterators.
///
/// See [`clamped_zip_1x2`] for more information.
pub struct ClampedZip1x2<R0, O0, O1, D0, D1>
where
    R0: Iterator,
    O0: Iterator,
    O0::Item: Clone,
    O1: Iterator,
    O1::Item: Clone,
    D0: Fn() -> O0::Item,
    D1: Fn() -> O1::Item,
{
    r0: R0,
    o0: O0,
    o1: O1,
    o0_default_fn: D0,
    o1_default_fn: D1,

    o0_latest_value: Option<O0::Item>,
    o1_latest_value: Option<O1::Item>,
}

impl<R0, O0, O1, D0, D1> Iterator for ClampedZip1x2<R0, O0, O1, D0, D1>
where
    R0: Iterator,
    O0: Iterator,
    O0::Item: Clone,
    O1: Iterator,
    O1::Item: Clone,
    D0: Fn() -> O0::Item,
    D1: Fn() -> O1::Item,
{
    type Item = (R0::Item, O0::Item, O1::Item);

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        let r0_next = self.r0.next()?;
        let o0_next = self.o0.next().or(self.o0_latest_value.take());
        let o1_next = self.o1.next().or(self.o1_latest_value.take());

        self.o0_latest_value = o0_next.clone();
        self.o1_latest_value = o1_next.clone();

        Some((
            r0_next,
            o0_next.unwrap_or_else(|| (self.o0_default_fn)()),
            o1_next.unwrap_or_else(|| (self.o1_default_fn)()),
        ))
    }
}
```

---

Part of a PR series to completely revamp the data APIs in preparation
for the removal of instance keys and the introduction of promises:
- #5573
- #5574
- #5581
- #5605
- #5606
- #5633
- #5673
- #5679
- #5687
- #5755
- TODO
- TODO

Builds on top of the static data PR series:
- #5534
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