multimethod.js | |
|---|---|
| multimethod.js 0.1.0 2 | 3 |(c) 2011 Kris Jordan 4 | 5 |
| (function() { |
| Multimethods are a functional programming control structure for dispatching 8 | function calls with user-defined criteria that can be changed at run time. 9 | Inspired by clojure's multimethods, multimethod.js provides an alternative to 10 | classical, prototype-chain based polymorphism. | |
Internal Utility Functions | |
| No operation function used by default by | var noop = function() {}; |
| Identity | var identity = function(a) { return a; }; |
| A | var indexOf = function(value, methods) {
14 | for(var i in methods) {
15 | var matches = methods[i][0];
16 | if(_(value).isEqual(matches)) {
17 | return i;
18 | }
19 | }
20 | return false;
21 | } |
| Given a dispatch | var match = function(value, methods) {
23 | var index = indexOf(value, methods);
24 | if(index !== false) {
25 | return methods[index][1];
26 | } else {
27 | return false;
28 | }
29 | } |
| Simple, consistent helper that returns a native value or invokes a function
30 | and returns its return value. Used by | var toValue = function(subject, args) {
32 | if(_.isFunction(subject)) {
33 | return subject.apply(this, args);
34 | } else {
35 | return subject;
36 | }
37 | }; |
| Plucking a single property value from an object in | var pluck = function(property) {
40 | return function(object) {
41 | return object[property];
42 | }
43 | }; |
Implementation | |
|
| var multimethod = function(dispatch) { |
Private Properties | |
|
| var _dispatch, |
|
| _methods = [], |
|
| _default = noop; |
| The fundamental control flow of the | var _lookup = function() {
52 | var criteria = _dispatch.apply(this, arguments),
53 | method = match(criteria, _methods);
54 | if(method !== false) {
55 | return method;
56 | } else {
57 | return _default;
58 | }
59 | }; |
| The result of calling | var returnFn = function() {
60 | var method = _lookup.apply(this, arguments);
61 | return toValue.call(this, method, arguments);
62 | }; |
Member Methods / API | |
|
| returnFn['dispatch'] = function(dispatch) {
65 | if(_.isFunction(dispatch)) {
66 | _dispatch = dispatch;
67 | } else if(_.isString(dispatch)) {
68 | _dispatch = pluck(dispatch);
69 | } else {
70 | throw "dispatch requires a function or a string.";
71 | }
72 | return this;
73 | } |
| If | returnFn.dispatch(dispatch || identity); |
|
| returnFn['when'] = function(matchValue, fn) {
77 | var index = indexOf(matchValue, _methods);
78 | if(index !== false) {
79 | _methods[index] = [matchValue, fn];
80 | } else {
81 | _methods.push([matchValue, fn]);
82 | }
83 | return this;
84 | } |
|
| returnFn['remove'] = function(matchValue) {
85 | var index = indexOf(matchValue, _methods);
86 | if(index !== false) {
87 | _methods.splice(index, 1);
88 | }
89 | return this;
90 | } |
|
| returnFn['default'] = function(method) {
93 | _default = method;
94 | return this;
95 | } |
| Our | return returnFn;
96 | }; |
| The following snippet courtesy of underscore.js.
97 | Export | if (typeof exports !== 'undefined') {
98 | if (typeof module !== 'undefined' && module.exports) {
99 | exports = module.exports = multimethod;
100 | var _ = require('underscore');
101 | }
102 | exports.multimethod = multimethod;
103 | } else if (typeof define === 'function' && define.amd) {
104 | define('multimethod', function() {
105 | return multimethod;
106 | });
107 | } else {
108 | this['multimethod'] = multimethod;
109 | var _ = this['_'];
110 | }
111 |
112 | multimethod.version = '0.1.0';
113 |
114 | }).call(this);
115 |
116 | |