This crate does not require nor std nor alloc. You're welcome ❤️

Intertop between generic_array and nalgebra, for const usize-hidden array storages.

This crate will presumably become obsolete, once const generics are introduced, but until then - feel free to unitize it.

NOTE: nalgebra's storage traits are fundamentally unsafe, so there is unsafe code inside, lints mentioned in Cargo.toml are there just for extra self-control.

Adding to a project

# Cargo.toml
[dependencies]
generic_array_storage = { git = "https://github.com/Dzuchun/generic_array_storage.git", branch = "master" }

Contribution

Just open an issue/PR or something. I'm happy to discuss any additions/fixes!

Context

What is typenum?

typenum implements integer operations as types. Basically, it allows for const arithmetic through same sort of trait wizardry, or something 🤷.

The takeaway is:

• if type A represents integer x
• and type B represents integer y

then

• <A typenum::marker_traits::Unsigned>::{U8, U16, .., I8, I16, ..} are associated constants equal to x (if possible)
• (same for B and y)
• typenum::operator_aliases::Sum<A, B> represents integer x + y
• typenum::operator_aliases::Prod<A, B> represents integer x * y

etc

What is generic_array?

generic_array implements arrays sized via ArrayLength trait implementors. Namely, it is implemented for typenum types, allowing creation an arrays sized as sum of two other arrays:

# use generic_array::{sequence::Concat, GenericArray};
// some normal rust arrays
let arr1: [i32; 3] = [1, 2, 3];
let arr2: [i32; 2] = [3, 5];

// some less-normal `generic_array` arrays
// (but having the same size and still stack-allocated)
let garr1 = GenericArray::from_array(arr1);
let garr2 = GenericArray::from_array(arr2);

// array concatenation
let garr_concat = GenericArray::concat(garr1, garr2);

// back to normal rust arrays
let concat: [i32; 5] = garr_concat.into_array();
// let concat: [i32; 6] = garr_concat.into_array(); // <-- does not compile!

Coolest thing is - this code is panic-free, fully statically checked, and missized arrays will result in compilation error.

What is nalgebra?

nalgebra is a matrix manipulation library, abstracted over type actually storing the elements. This allows matrices to be automatically stored on stock, if their dimensions can be inferred at compile-time.

Generally, to store the entire matrix on stack, you'll need for both of it's dimensions to be known, like nalgrabra::U2 or nalgebra::U3. Unfortunately, default storage provided by nalgebra has a const usize type parameters, so they can't be used in case of sizes provided by associated constants.

What is generic_array_storage?

This crate provides implementation of traits defining nalgebra storage backed up by generic_array arrays. This allows creation of matrices having dimensions fully expressed as types, completely removing need for const usize.

For ease of use, there's a GenericMatrix type alias, and GenericMatrixExt extension trait, providing convenient type interface and conversion functions respectively. Note that GenericMatrix is an alias to nalgebra::Matrix, so all of the functions provided by nalgebra are expected to be supported.