reductor 0.0.2

Generic abstractions for combining and nesting reduction patterns for iterables.

The main entry point to this library is Reduce::reduce_with, which can be called on any Iterator, and is very similar to Iterator::reduce, but uses 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(sum) = iter.clone().reduce_with::<Sum<u32>>();
let Product(product) = iter.clone().reduce_with::<Product<u32>>();
let Count(count) = iter.clone().reduce_with();
assert_eq!(sum, iter.clone().sum());
assert_eq!(product, iter.clone().product());
assert_eq!(count, iter.clone().count());

let Max(max) = iter.clone().reduce_with::<Max<Option<u32>>>();
let Min(min) = iter.clone().reduce_with::<Min<Option<u32>>>();
assert_eq!(max, Some(9));
assert_eq!(min, Some(0));

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

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

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

use reductor::{Reduce, ReductorPair, Sum, Max};

let iter = 0..10;
let ReductorPair(Max(max), Sum(sum)) = iter
    .clone()
    .map(|x| x)
    .reduce_with::<Option<ReductorPair<Max<usize>, Sum<usize>>>>().unwrap();

assert_eq!(sum, iter.clone().sum());
assert_eq!(max, iter.clone().max().unwrap());

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

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

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

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