type-vec: a type-safe vector with type-level length in Rust

Usage

Include the crate in your Cargo.toml.

type-vec = "0.1"

Features

The type-safe vector type

The vector type has a type-level length, which length can be either dynamic or static. That is, the length can be given in compile time or is only known in runtime.

use type_vec::{Vect, Dyn};
use typenum::consts::*; // imports U0

// vector with static length
let vec = Vect::<usize, U0>::new();

// vector with dynamic length
let vec = Vect::<usize, Dyn>::new();

Type-inferred and type-checked vector operations

The vector supports common operations, such as push, pop and insert. The output length is inferred in compile time on each vector operation. Thus, you can gain the benefit of type safety to avoid common errors.

use type_vec::Vect;
use typenum::consts::*;

let vec = Vect::<usize, U0>::new();
let vec: Vect<usize, U1> = vec.push(3);
let vec: Vect<usize, U2> = vec.push(1);

// This line does not compile due to incorrect output length assumption.
/* let vec: Vect<usize, U2> = vec.push(1); */

// You can omit the type annotation and leave it to compiler
let (vec, item) = vec.pop();
let (vec, item) = vec.pop();

// This line causes compile error because we cannot pop an empty vector.
/* let vec = vec.pop(); */

Zero-abstraction and efficient implementation

The design promises zero-abstraction. Whenever the length is known in compile time, it picks the more efficient implementation. Let's see the element accessing using get. If the index is static, The index is checked against the length in compile time, and returns the element directly if it compiles. Otherwise, it returns an Option<&T> like usual [Vec].

use type_vec::Vect;
use typenum::consts::*;

let vec = Vect::<usize, U0>::new();
let vec: Vect<usize, U1> = vec.push(3);
let vec: Vect<usize, U2> = vec.push(1);
let vec: Vect<usize, U3> = vec.push(4);

// get element by static index
// the index is checked in compile time and returns the element directly
let elem = vec.get(U1::new());
assert_eq!(elem, &1);

// get element by dynamic index
// it returns an `Option` depending on the index
let elem = vec.get(1);
assert_eq!(elem, Some(&1));

How it works

The construction of the vector type heavily relies on the TYP type-level programming langauge. It enables complex type-level computation done by simple Rusty syntax. Those interested can read the TYP book.

License

MIT license. See the LICENSE file.