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Multiple dispatch in JavaScript
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| function isType (type) { | |
| return function (arg) { | |
| return typeof(arg) === type; | |
| }; | |
| } | |
| function instanceOf (clazz) { | |
| return function (arg) { | |
| return arg instanceof clazz; | |
| }; | |
| } | |
| function isPrototypeOf (proto) { | |
| return Object.prototype.isPrototypeOf.bind(proto); | |
| } | |
| function MatchTypes () { | |
| var matchers = [].slice.call(arguments, 0, arguments.length - 1), | |
| body = arguments[arguments.length - 1]; | |
| function typeChecked () { | |
| var i, | |
| arg, | |
| value; | |
| if (arguments.length != matchers.length) return; | |
| for (i in arguments) { | |
| arg = arguments[i]; | |
| if (!matchers[i].call(this, arg)) return; | |
| } | |
| value = body.apply(this, arguments); | |
| return value === undefined | |
| ? null | |
| : value; | |
| } | |
| return imitate(body, typeChecked); | |
| } | |
| ////////// EXAMPLE ////////// | |
| function Fighter () {}; | |
| function Meteor () {}; | |
| var handlesManyCases = Match( | |
| MatchTypes( | |
| instanceOf(Fighter), instanceOf(Meteor), | |
| function (fighter, meteor) { | |
| return "a fighter has hit a meteor"; | |
| } | |
| ), | |
| MatchTypes( | |
| instanceOf(Fighter), instanceOf(Fighter), | |
| function (fighter, fighter) { | |
| return "a fighter has hit another fighter"; | |
| } | |
| ), | |
| MatchTypes( | |
| instanceOf(Meteor), instanceOf(Fighter), | |
| function (meteor, fighters) { | |
| return "a meteor has hit a fighter"; | |
| } | |
| ), | |
| MatchTypes( | |
| instanceOf(Meteor), instanceOf(Meteor), | |
| function (meteor, meteor) { | |
| return "a meteor has hit another meteor"; | |
| } | |
| ) | |
| ); | |
| handlesManyCases(new Meteor(), new Meteor()); | |
| //=> 'a meteor has hit another meteor' | |
| handlesManyCases(new Fighter(), new Meteor()); | |
| //=> 'a fighter has hit a meteor' | |
| ////////// Multiple Dispatch for Methods ////////// | |
| var FighterPrototype = {}, | |
| MeteorPrototype = {}; | |
| FighterPrototype.crashInto = Match( | |
| MatchTypes( | |
| isPrototypeOf(FighterPrototype), | |
| function (fighter) { | |
| return "fighter(fighter)"; | |
| } | |
| ), | |
| MatchTypes( | |
| isPrototypeOf(MeteorPrototype), | |
| function (fighter) { | |
| return "fighter(meteor)"; | |
| } | |
| ) | |
| ); | |
| MeteorPrototype.crashInto = Match( | |
| MatchTypes( | |
| isPrototypeOf(FighterPrototype), | |
| function (fighter) { | |
| return "meteor(fighter)"; | |
| } | |
| ), | |
| MatchTypes( | |
| isPrototypeOf(MeteorPrototype), | |
| function (meteor) { | |
| return "meteor(meteor)"; | |
| } | |
| ) | |
| ); | |
| var someFighter = Object.create(FighterPrototype), | |
| someMeteor = Object.create(MeteorPrototype); | |
| someFighter.crashInto(someMeteor); | |
| //=> 'fighter(meteor)' |
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| function nameAndLength(name, length, body) { | |
| var abcs = [ 'q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p', | |
| 'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', | |
| 'z', 'x', 'c', 'v', 'b', 'n', 'm' ], | |
| pars = abcs.slice(0, length), | |
| src = "(function " + name + " (" + pars.join(',') + ") { return body.apply(this, arguments); })"; | |
| return eval(src); | |
| } | |
| function imitate(exemplar, body) { | |
| return nameAndLength(exemplar.name, exemplar.length, body); | |
| } | |
| function getWith (prop, obj) { | |
| function gets (obj) { | |
| return obj[prop]; | |
| } | |
| return obj === undefined | |
| ? gets | |
| : gets(obj); | |
| } | |
| function mapWith (fn, mappable) { | |
| function maps (collection) { | |
| return collection.map(fn); | |
| } | |
| return mappable === undefined | |
| ? maps | |
| : maps(collection); | |
| } | |
| function pluckWith (prop, collection) { | |
| var plucker = mapWith(getWith(prop)); | |
| return collection === undefined | |
| ? plucker | |
| : plucker(collection); | |
| } | |
| function Match () { | |
| var fns = [].slice.call(arguments, 0), | |
| lengths = pluckWith('length', fns), | |
| length = Math.min.apply(null, lengths), | |
| names = pluckWith('name', fns).filter(function (name) { return name !== ''; }), | |
| name = names.length === 0 | |
| ? '' | |
| : names[0]; | |
| return nameAndLength(name, length, function () { | |
| var i, | |
| value; | |
| for (i in fns) { | |
| value = fns[i].apply(this, arguments); | |
| if (value !== undefined) return value; | |
| } | |
| }); | |
| } |
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Extracted from JavaScript Spessore.