Mitsein is a Rust library that provides strongly typed APIs for non-empty and ordered collections and views, including (but not limited to) iterators, slices, and vectors.

Basic Usage

Allocating a Vec1 from one or more items (infallibly):

use mitsein::prelude::*;

let xs = Vec1::from_one(0i32);
let xs = Vec1::from([0i32, 1, 2]);
let xs = Vec1::from_head_and_tail(0i32, [1, 2]);

let xs: Vec1<_> = [0i32].into_iter1().collect1();

let xs = vec1![0i32, 1, 2];

Allocating a Vec1 from zero or more items (fallibly):

use mitsein::prelude::*;

let ys = vec![0i32, 1, 2];

let xs = Vec1::try_from(ys).unwrap();
let xs = Vec1::try_from(&[0i32, 1, 2]).unwrap();
let xs = Vec1::try_from_iter([0i32, 1, 2]).unwrap();

let xs: Vec1<_> = [0i32].into_iter().try_collect1().unwrap();

Mapping over items in a Vec1:

use mitsein::prelude::*;

let xs = Vec1::from([0i32, 1, 2]);
let ys: Vec1<_> = xs.into_iter1().map(|x| x + 1).collect1();

Removing items from a Vec1:

use mitsein::prelude::*;

let mut xs = Vec1::from([0i32, 1, 2]);
while let Ok(item) = xs.pop_or().only() { ... }

let mut xs = Vec1::from([0i32, 1, 2]);
xs.tail().clear();

Bridging between Iterator and Iterator1:

use mitsein::iter1;
use mitsein::prelude::*;

let xs = iter1::head_and_tail(0i32, [1, 2]);
let xs: Vec1<_> = xs.into_iter().skip(3).or_non_empty([3]).collect1();
assert_eq!(xs.as_slice(), &[3]);

Features and Comparisons

Non-empty iterator APIs separate concerns using familiar patterns and syntax. Mitsein need not expose combinatorial sets of inherent iterator-like functions in non-empty collections. For example, the vec1 crate supports map operations over its Vec1 type via the Vec1::mapped, Vec1::mapped_ref, and Vec1::mapped_mut functions. Mitsein instead exposes map operations via Iterator1, which can support any non-empty view or collection with a more typical API (e.g., Iterator1::map).

Non-empty slice APIs enable borrowing and copy-on-write, so Mitsein supports the standard Cow type, unlike other non-empty Vec implementations like the nonempty and vec1 crates.

Items are stored consistently in Mitsein. No head item is allocated differently. For example, the nonempty crate directly exposes a head item that is, unlike tail items, not allocated on the heap. This can potentially cause surprising behavior or performance and precludes constructing slices over nominally contiguous collections.

Non-empty collection APIs that exhibit different behavior from their counterparts have distinct names in Mitsein. For example, the vec1 crate presents Vec1::pop and Vec1::remove, which may be unclear in context. Mitsein instead presents more explicit APIs like Vec1::pop_or, which returns a TakeOr that determine what to do when only one item remains. This leads to more explicit expressions like xs.pop_or().only() and xs.remove_or(1).replace_only(0).

Mitsein separates many non-empty error concerns into a segmentation API. Segments span a range in a collection and support the insertion and removal of items. Non-empty collections can be segmented prior to removals, which consolidates error conditions: the segment can be freely manipulated without checks or errors after it has been constructed. The nonempty and nunny crates have limited or no support for removals while the vec1 crate only supports fallible removals directly against Vec1.

use mitsein::prelude::*;

let mut xs = Vec1::from([0i32, 1, 2, 3, 4]);
xs.tail().clear();
assert_eq!(xs.as_slice(), &[0i32]);

let mut xs = Vec1::from([0i32, 1, 2, 3, 4]);
xs.tail().rtail().swap_drain(..);
assert_eq!(xs.as_slice(), &[0i32, 4]);

let mut xs = Vec1::from([0i32, 1, 2, 3, 4]);
let mut xss = xs.segment(1..);
xss.truncate(2);
xss.remove_back(); // `remove_back` is the counterpart to `pop`.
assert_eq!(xs.as_slice(), &[0i32, 1]);

Mitsein provides comprehensive coverage of ordered collections and container APIs in core and alloc. This notably includes slice, BTreeMap, BTreeSet, Box, and Arc. The nonempty and vec1 crates lack support for primitive types like slice and collections other than Vec.

Mitsein is a no_std library and alloc is optional. Non-empty slices, iterators, and arrays can be used in contexts where OS features or allocation are not available. Integration with arrayvec also functions in no_std environments.

Integrations and Cargo Features

Mitsein provides some optional features and integrations via the following Cargo features.

Feature	Default	Primary Dependency	Description
alloc	No	alloc	Non-empty collections that allocate, like Vec1.
arrayvec	No	arrayvec	Non-empty implementation of ArrayVec.
itertools	No	itertools	Combinators from itertools for Iterator1.
serde	No	serde	De/serialization of non-empty collections with serde.
std	Yes	std	Integrations with std::io.