Trait Aggregator

Source

pub trait Aggregator:
    Default
    + Debug
    + Clone
    + 'static {
    type Input: InputBounds;
    type MutablePartialAggregate: MutablePartialAggregateType;
    type PartialAggregate: PartialAggregateType;
    type Aggregate: Debug + Send;

    const IDENTITY: Self::PartialAggregate;

    // Required methods
    fn lift(input: Self::Input) -> Self::MutablePartialAggregate;
    fn combine_mutable(
        a: &mut Self::MutablePartialAggregate,
        input: Self::Input,
    );
    fn freeze(a: Self::MutablePartialAggregate) -> Self::PartialAggregate;
    fn combine(
        a: Self::PartialAggregate,
        b: Self::PartialAggregate,
    ) -> Self::PartialAggregate;
    fn lower(a: Self::PartialAggregate) -> Self::Aggregate;

    // Provided methods
    fn combine_inverse() -> Option<InverseFn<Self::PartialAggregate>> { ... }
    fn combine_simd() -> Option<CombineSimdFn<Self::PartialAggregate>> { ... }
    fn compression() -> Option<Compression<Self::PartialAggregate>> { ... }
}

Expand description

Aggregation interface that library users must implement to use µWheel

µWheel provides a bunch of pre-defined aggregator implementations including:

§Example

Here is a simple example showing how to create a SUM aggregator using u32.

use uwheel::Aggregator;

#[derive(Default, Debug, Clone)]
struct MySumAggregator;

impl Aggregator for MySumAggregator {
    const IDENTITY: Self::PartialAggregate = 0u32;
    type Input = u32;
    type MutablePartialAggregate = u32;
    type Aggregate = u32;
    type PartialAggregate = u32;

    fn lift(input: Self::Input) -> Self::MutablePartialAggregate {
       input.into()
    }

    fn combine_mutable(a: &mut Self::MutablePartialAggregate, input: Self::Input) {
       *a += input;
    }

    fn freeze(a: Self::MutablePartialAggregate) -> Self::PartialAggregate {
       a.into()
    }

    fn combine(a: Self::PartialAggregate, b: Self::PartialAggregate) -> Self::PartialAggregate {
       a + b
    }

    fn lower(a: Self::PartialAggregate) -> Self::Aggregate {
       a
    }
}

Required Associated Constants§

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const IDENTITY: Self::PartialAggregate

Identity value for Self::PartialAggregate.

For example, for SUM types the identity value should be set to 0.

Required Associated Types§

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type Input: InputBounds

Aggregator Input type that can be converted or applied to a Self::MutablePartialAggregate.

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type MutablePartialAggregate: MutablePartialAggregateType

Mutable Partial Aggregate type that can be mutated above µWheel’s low watermark.

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type PartialAggregate: PartialAggregateType

Immutable Partial Aggregate type that defines aggregates below µWheel’s low watermark.

Source

type Aggregate: Debug + Send

Final Aggregate type that can be lowered from a Self::PartialAggregate.

In many cases the Self::PartialAggregate type will be the same as Self::Aggregate. An instance where it is not is an AVG function where the partial aggregate consists of a (sum, count) tuple and the final aggregate “average” is calculated through sum/count.