https://github.com/bcherny/lazy-arr
Arrays that look just like regular JavaScript arrays, but are computed lazily.
https://github.com/bcherny/lazy-arr
array lazy stream swift
Last synced: 6 months ago
JSON representation
Arrays that look just like regular JavaScript arrays, but are computed lazily.
- Host: GitHub
- URL: https://github.com/bcherny/lazy-arr
- Owner: bcherny
- Created: 2017-06-07T14:06:21.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2017-06-09T07:34:50.000Z (over 8 years ago)
- Last Synced: 2024-12-17T03:03:24.048Z (10 months ago)
- Topics: array, lazy, stream, swift
- Language: TypeScript
- Homepage: https://performancejs.com/post/ewffd34/Introducing:-Lazy-arrays-in-JavaScript
- Size: 8.79 KB
- Stars: 65
- Watchers: 3
- Forks: 2
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# lazy-arr [![Build Status][build]](https://circleci.com/gh/bcherny/lazy-arr) [![npm]](https://www.npmjs.com/package/lazy-arr) [![mit]](https://opensource.org/licenses/MIT)
[build]: https://img.shields.io/circleci/project/bcherny/lazy-arr.svg?branch=master&style=flat-square
[npm]: https://img.shields.io/npm/v/lazy-arr.svg?style=flat-square
[mit]: https://img.shields.io/npm/l/lazy-arr.svg?style=flat-square
> Arrays that look just like regular JavaScript arrays, but are computed lazily. Like Scala or Haskell's lazy streams. Read more about it in the introductory blog post: https://performancejs.com/post/ewffd34/Introducing:-Lazy-arrays-in-JavaScript.
## Install
```sh
npm i lazy-arr -S
```
## Usage
Lazy-arr takes a function, and uses it to lazily generate values for the array. The function takes a numerical array index (eg. `5`) and should return the value for that index in the array. The function doesn't have to be idempotent, but its return value *will* be cached (you can then delete it from cache, if you want).
It supports 2 usage patterns:
1. Call it with just a function:
```js
import { lazy } from 'lazy-arr'
lazy(index => index + 1)
```
2. Call it with a function and an initial value:
```js
import { lazy } from 'lazy-arr'
let seq = lazy([0])(index => index + seq[index - 1])
```
## Examples
```js
import { lazy } from 'lazy-arr'
// even numbers
let numbers = lazy(_ => _ * 2)
numbers[0] // 0
numbers[5] // 10
// fibonacci numbers (with initial value of [0, 1])
let fibs = lazy([0, 1])(_ => fibs[_ - 1] + fibs[_ - 2])
fibs[0] // 0
fibs[1] // 1
fibs[10] // 55
```
## Other operations
```js
import { lazy } from 'lazy-arr'
let numbers = lazy(_ => _ * 2)
numbers[3] // 6
// membership
2 in numbers // true
3 in numbers // true
4 in numbers // false
// deleting
delete numbers[3]
3 in numbers // false
```
Note that you *cannot* directly set values:
```js
import { lazy } from 'lazy-arr'
let numbers = lazy(_ => _ * 2)
numbers[7] = 3 // THROWS ERROR
```
## License
MIT