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    3.0.2 • Public • Published

    Generic Functions for JavaScript

    It's time to bring something new old to JavaScript: generic functions!


    Polymorphism in JavaScript is changing:

    What are Generic Functions?

    Generic functions were popularized in the Common Lisp Object System, published in 1988.

    A generic function has a single signature (or interface) and multiple implementations, called methods. Unlike in OOP, the methods are specialized across all of the function arguments, not just the first one.

    For example, the signature may be:

    map(mapper, collection)

    It may have different implementations based on the type of the collection:

    const mapMethod = (callback, array) =>;
    const mapMethod = (callback, set) =>
      new Set([...set].map(callback));

    It may also have a method that takes a lookup table instead of a callback function:

    const mapMethod = (table, array) => => table[value]);

    In fact we could support lookup tables for every type of collection by adding a method that calls itself recursively like this:

    const mapMethod = (table, collection) =>
      map((value) => table[value], collection);


    Here's how you could implement the above example using the library.

    const assert = require(`@nodeguy/assert`);
    const generic = require('@nodeguy/generic')
    const _ = generic._;
    const map = generic.function();
    map.method([m => typeof m === "function", Array.isArray], (callback, array) =>
      [m => typeof m === "function", c => c instanceof Set],
      (callback, set) => new Set([...set].map(callback))
    map.method([m => typeof m === "object", _], (table, collection) =>
      map(value => table[value], collection)
    assert.deepEqual(map(Math.sqrt, [1, 4, 9]), [1, 2, 3]);
    assert.deepEqual(map(Math.sqrt, new Set([1, 4, 9])), new Set([1, 2, 3]));
    assert.deepEqual(map({ 1: 1, 4: 2, 9: 3 }, [1, 4, 9]), [1, 2, 3]);
      map({ 1: 1, 4: 2, 9: 3 }, new Set([1, 4, 9])),
      new Set([1, 2, 3])

    See test/index.js for more usage examples.


    $ npm install @nodeguy/generic


    Copyright 2016 David Braun

    Licensed under the Apache License, Version 2.0 (the "License"); you may not use these files except in compliance with the License. You may obtain a copy of the License at Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


    npm i @nodeguy/generic

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