[Idea]: add support for boolean arrays in stdlib

[kgryte]

Idea

Currently, stdlib supports a variety of array data types; however, most of these data types are numeric. The lone exception is the "generic" data type for use with generic arrays.

A need exists to expand data type support beyond numeric data types (e.g., real and complex floating-point, signed and unsigned integer) to include other non-numeric data types. One such data type is a boolean data type. The rationale for having a dedicated boolean data type is for use in advanced array indexing, where a boolean array can be used to filter/mask another array. See, e.g., the examples in @stdlib/array/to-fancy.

Accordingly, the goal of this project is to create a new typed array called a BooleanArray, which will only support the values true and false. This new array type should follow a similar path to that of @stdlib/array/complex64, which provides a typed array dedicated to single-precision complex floating-point numbers; namely, BooleanArray should support standard typed array methods, as well as provide accessors for getting and setting array elements.

Note, however, that a BooleanArray should be a typed array (meaning, fixed length with a fixed memory layout). A BooleanArray should not wrap a "generic" array. Instead, the array should be backed by a Uint8Array, similar to how @stdlib/array/complex64 is backed by a Float32Array.

As part of this project, not only will a new BooleanArray be added to the project, but it will be integrated throughout stdlib. This will entail adding support for BooleanArrays wherever arrays are accepted/used, following the same precedent established by @stdlib/array/complex64 and other custom array types in stdlib. This includes adding support for boolean arrays in ndarray APIs.

Expected outcomes

The expected outcomes of this idea should be (1) creation of a new @stdlib/array/bool package exposing a new typed array constructor, (2) support for BooleanArray instances throughout @stdlib/array/*, (3) support for BooleanArray instances as backing arrays for ndarrays (which may involve working with various C APIs), and (4) any other integration opportunities.

Status

Some initial work has been done to create a new @stdlib/array/bool package, but this is incomplete and needs more significant investment. There exists prior art for adding custom typed arrays to stdlib; namely, Complex64Array and Complex128Array.

Involved software

No special software for initial work. Once work has progressed to ndarray support, will need access to a C compiler, as documented in the project development guide.

Technology

JavaScript, C, nodejs, native addons

Other technology

n/a

Difficulty

Intermediate/Advanced

Difficulty justification

This project is ambitious, as arrays are fundamental to a lot of stdlib functionality; however, many of the more difficult integration aspects have already addressed given the widespread support for accessor arrays throughout the project. The main project difficulty beyond the creation of a new BooleanArray class will be finding all the various bits of code throughout the project which need to be updated.

Prerequisite knowledge

Familiarity and comfort with JavaScript would be highly recommended, given that this project will require considerable programming in JavaScript. Some familiarity with C would also be good, especially for boolean array integration with ndarrays.

Project length

350hrs, but can scope can be tailored depending on contributor ability. A contributor proficient in JavaScript can probably finish a @stdlib/array/bool package within 90hrs. Integration work is likely to take longer.

Potential mentors

@kgryte @Planeshifter

[kgryte]

This idea was completed during GSoC 2024.