How to use @arrows/multimethod - 10 common examples

const { multi, method, fromMulti } = require('@arrows/multimethod')

/**
 * Function where the priority does matter
 *
 * @param {number} points
 * @returns {number} grade
 */
const baseGradeExam = multi(
  method((points) => points < 10, 'failed'),
  method((points) => points <= 15, 'ok'),
  method((points) => points > 15, 'good'),
)

const gradeExam = fromMulti(
  method((points) => points === 0, 'terrible'),
  method((points) => points > 20, 'excellent'),
)(baseGradeExam)

console.log(
  gradeExam(0), // -> 'terrible'
  gradeExam(5), // -> 'failed'
  gradeExam(10), // -> 'ok'
  gradeExam(15), // -> 'ok'
  gradeExam(20), // -> 'good'
  gradeExam(25), // -> 'excellent'
)

const { curry } = require('@arrows/composition')
const { multi, method } = require('@arrows/multimethod')

/**
 * Currying with a generic `curry` function.
 * Explicit dispatch function (length: 2).
 *
 * Note that you can still use non-functions as corresponding values.
 *
 * @param {string} type
 * @param {string} source
 * @returns {string} info
 */
const play = multi(
  (type, source) => type,
  method('audio', (type, source) => `Playing audio from: ${source}`),
  method('video', (type, source) => `Playing video from: ${source}`),
)

const curriedPlay = curry(play)

const playAudio = curriedPlay('audio')
const playVideo = curriedPlay('video')

console.log(
  playAudio('songs.io/123'), // -> "Playing audio from: songs.io/123"
  playVideo('movies.com/123'), // -> "Playing video from: movies.com/123"
)

* @param {object} data
 * @param {string} format
 * @returns {void}
 */
const save = multi(
  (data, format) => format, // Custom dispatch function

  method('json', (data, format) => {
    console.log('Saving as JSON!')
  }),

  method('html', (data, format) => {
    console.log('Saving as HTML!')
  }),

  method((data, format) => {
    console.log('Default - saving as TXT!')
  }),
)

const data = { name: 'Alice', score: 100 }

save(data, 'json') // -> "Saving as JSON!"
save(data, 'html') // -> "Saving as HTML!"
save(data, 'csv') // -> "Default - saving as TXT!"

const extendedSave = method('csv', (data, format) => {
  console.log('Saving as CSV!')
})(save)

extendedSave(data, 'json') // -> "Saving as JSON!"
extendedSave(data, 'html') // -> "Saving as HTML!"

* matched using the constructor algorithm, other values of the array
 * will be matched using a deep strict equal algorithm.
 *
 * The algorithm, by design, checks for constructors only the first-level array.
 *
 * It can be very useful, for example as a trivial alternative
 * to otherwise complex visitor patter.
 *
 * @param {Object} document
 * @param {Object} template
 * @returns {string} embedding description
 */
const embed = multi(
  method([Article, PDF], 'Embedding article inside PDF'),
  method([Article, HTML], 'Embedding article inside HTML'),
  method([Recipe, PDF], 'Embedding recipe inside PDF'),
  method([Recipe, HTML], 'Embedding recipe inside HTML'),
)

console.log(
  embed(new Article(), new PDF()), // -> "Embedding article inside PDF"
  embed(new Recipe(), new HTML()), // -> "Embedding recipe inside HTML"
)

/**
 * Function with multiple arguments,
 * default dispatch will return the array of arguments.
 *
 * Note that the order of the arguments does matter,
 * so if you want the example to work for each combination,
 * you either have to provide methods for reversed arguments
 * or add your custom dispatch function,
 * which returns sorted values (better option).
 *
 * @param {string} colorA
 * @param {string} colorB
 * @returns {string} the resulting color
 */
const mixLights = multi(
  method(['red', 'green'], 'yellow'),
  method(['red', 'blue'], 'magenta'),
  method(['green', 'blue'], 'cyan'),
)

console.log(
  mixLights('red', 'blue'), // -> "magenta"
  // mixLights('blue', 'red'), // -> throws an error
)

const { multi, method } = require('@arrows/multimethod')

/**
 * Function with a single argument,
 * default dispatch will return that argument as-is.
 *
 * @param {string} color
 * @returns {string} hex color
 */
const colorToHex = multi(
  method('red', '#ff0000'),
  method('green', '#00ff00'),
  method('blue', '#0000ff'),
)

console.log(
  colorToHex('green'), // -> "#00ff00"
)

const extendedSave = method('csv', (data, format) => {
  console.log('Saving as CSV!')
})(save)

extendedSave(data, 'json') // -> "Saving as JSON!"
extendedSave(data, 'html') // -> "Saving as HTML!"
extendedSave(data, 'csv') // -> "Saving as CSV!"
extendedSave(data, 'yaml') // -> "Default - saving as TXT!"

const extendedSave2 = fromMulti(
  method('csv', (data, format) => {
    console.log('Saving as CSV!')
  }),

  method('yaml', (data, format) => {
    console.log('Saving as YAML!')
  }),
)(save)

extendedSave2(data, 'json') // -> "Saving as JSON!"
extendedSave2(data, 'html') // -> "Saving as HTML!"
extendedSave2(data, 'csv') // -> "Saving as CSV!"
extendedSave2(data, 'yaml') // -> "Saving as YAML!"

const { multi, method } = require('@arrows/multimethod')

/**
 * Currying with a generic `curry` function.
 * Explicit dispatch function (length: 2).
 *
 * Note that you can still use non-functions as corresponding values.
 *
 * @param {string} type
 * @param {string} source
 * @returns {string} info
 */
const play = multi(
  (type, source) => type,
  method('audio', (type, source) => `Playing audio from: ${source}`),
  method('video', (type, source) => `Playing video from: ${source}`),
)

const curriedPlay = curry(play)

const playAudio = curriedPlay('audio')
const playVideo = curriedPlay('video')

console.log(
  playAudio('songs.io/123'), // -> "Playing audio from: songs.io/123"
  playVideo('movies.com/123'), // -> "Playing video from: movies.com/123"
)

import { method, multi, Multi } from '@arrows/multimethod'
/**
 * Multimethod type defined using interface.
 *
 * Extending `Multi` type guarantees that the multimethod will
 * be recognized correctly when extended by `fromMulti` function.
 */

interface IMultiply extends Multi {
  (times: number, x: number): number
  (times: number, x: string): string
}

const multiply: IMultiply = multi(
  (times: number, x: any): string => typeof x,
  method('number', (times: number, x: number): number => x * times),
  method('string', (times: number, x: string): string => x.repeat(times)),
)

console.log(
  multiply(3, 3), // -> 9
  multiply(3, 'foo'), // -> "foofoofoo"
  // multiply(3, [1, 2, 3]), // compiler error
)

export { IMultiply }
export default multiply

console.log('todo removed')
  },
  toggle(id) {
    console.log('todo toggled')
  },
}

/**
 * Function with a custom dispatch.
 * Dispatch function can produce any arbitrary value.
 *
 * @param {Object} action
 * @param {Object} store
 * @returns {void}
 */
const handleAction = multi(
  (action, store) => action.type, // custom dispatch
  method('ADD_TODO', (action, store) => store.add(action.text)),
  method('REMOVE_TODO', (action, store) => store.remove(action.id)),
  method('TOGGLE_TODO', (action, store) => store.toggle(action.id)),
)

handleAction({ type: 'ADD_TODO', text: 'Eat banana.' }, store) // -> "todo added"
handleAction({ type: 'TOGGLE_TODO', id: 0 }, store) // -> "todo toggled"