Macro aggregate_struct 

macro_rules! aggregate_struct {
    (
        $ty_name:path {
            $($fields:ident: $aggregate_ops:expr,)+
            $(..$base_struct:expr)?
        }
    ) => { ... };
    (
        $ty_name:path {
            $($fields:ident: $aggregate_ops:expr),+
        }
    ) => { ... };
}

Available on crate feature unstable only.

Combines multiple aggregate ops into a single “struct-based” aggregate.

The struct can be constructed normally (even with a base struct), except every field is “initialized” with an AggregateOp whose Value matches that field’s type.

Among the specified fields to be aggregated, every field except the last one must implement RefAggregateOp.

Limitations

This macro currently supports structs with 1 to 12 aggregated fields (i.e., fields explicitly specified with an aggregate op, not those filled via a base struct such as ..Default::default()).

Examples

use std::collections::HashMap;
use better_collect::{
    prelude::*, aggregate_struct,
    aggregate::{self, AggregateOp, GroupMap},
};

#[derive(Debug, Default, PartialEq)]
struct Stats {
    sum: i32,
    max: i32,
    version: u32,
}

let groups = [(1, 1), (1, 4), (2, 1), (1, 2), (2, 3)]
    .into_iter()
    .better_collect(
        HashMap::new()
            .into_aggregate(aggregate_struct!(Stats {
                sum: aggregate::Sum::new().cloning(),
                max: aggregate::Max::new(),
                ..Default::default()
            }))
    );

let expected_groups = HashMap::from_iter([
    (1, Stats { sum: 7, max: 4, version: 0 }),
    (2, Stats { sum: 4, max: 3, version: 0 }),
]);
assert_eq!(groups, expected_groups);