Crate reductor

Generic abstractions for combining and nesting reduction patterns for iterables.

The main entry points to this library are Reduce::reduce_with and Reduce::fold_with, which can be called on any Iterator, and are similar to Iterator::reduce and Iterator::fold, respectively, but use a generic implementation of a Reductor for the reduction logic.

The following examples shows some of the basic building blocks from which reductor enables building more complex patterns:

use reductor::{Reduce, Sum, Product, Count, Min, Max};

let iter = 0..10;

let Sum::<u32>(sum) = iter.clone().reduce_with();
let Product::<u32>(product) = iter.clone().fold_with(2);
let Count(count) = iter.clone().reduce_with();
assert_eq!(sum, iter.clone().sum());
assert_eq!(product, iter.clone().product::<u32>() * 2);
assert_eq!(count, iter.clone().count());

let min: Option<Min<u32>> = iter.clone().reduce_with();
let Max::<Option<u32>>(max) = iter.clone().reduce_with();
assert_eq!(min.unwrap(), Min(iter.start));
assert_eq!(max.unwrap(), iter.last().unwrap());

Notice that unlike Sum and Product, Min and Max won’t reduce an empty iterator into the default value. This mirrors the way Iterator::max returns an Option<T>, unlike Iterator::sum.

Now, let’s combine two Reductors to reduce an iterator that produces a pair of values:

use reductor::{Reduce, Sum, Product};

let iter = 0..10;

let (Sum::<usize>(sum), Product::<usize>(product)) = iter
    .clone()
    .map(|x| (x, x * 2))
    .reduce_with();

assert_eq!(sum, iter.clone().sum());
assert_eq!(product, iter.map(|x| x * 2).product());

Another abstraction provided by this library is Reductors, which allows reducing an iterator producing a single value by a tuple of Reductors, in tandem.

use reductor::{Reduce, Reductors, Min, Max, Sum};

let iter = 0..10;

let Reductors((Min::<usize>(min), Max::<usize>(max))) = iter
    .clone()
    .reduce_with::<Option<_>>()
    .unwrap();

assert_eq!(min, iter.start);
assert_eq!(max, iter.end - 1);

let Reductors((Min::<Option<usize>>(min), Sum::<usize>(sum))) = iter
    .clone()
    .reduce_with();

assert_eq!(min.unwrap(), iter.start);
assert_eq!(sum, iter.sum());

These constructs allow building very complex iterator loops that compose numerous reductions into a single set of results.

use reductor::{Reduce, Reductors, Count, Sum, Max, Min};

let iter = (0_i32..100).filter_map(|x| {
    if x % 2 == 0 {
        None
    } else {
        Some((x, x.leading_zeros()))
    }
});

let Reductors((
    Count(count),
    (Sum::<i32>(sum), Reductors((Min::<u32>(min), Max::<u32>(max)))),
)) = iter.clone().reduce_with::<Option<_>>().unwrap();

assert_eq!(count, iter.clone().count());
assert_eq!(sum, iter.clone().map(|(x, ..)| x).sum());
assert_eq!(min, iter.clone().map(|(.., x)| x).min().unwrap());
assert_eq!(max, iter.map(|(.., x)| x).max().unwrap());

Re-exports

pub use reductors::*;

Modules

reductors

Standard implementations of Reductor.

Structs

Reductors

This struct can be used to run a tuple of Reductors on a single value, by cloning every element yielded, and updating all Reductors’ states in each iteration.

Traits

Reduce

Allow reducing an Iterator with a Reductor.

Reductor

Reductors are types that implement the logic for folding an iterator into a single result.