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| function createMultimethod(dispatch, noMatch) { | |
| if(typeof dispatch !== 'function') { | |
| throw new TypeError('dispatch must be a function'); | |
| } | |
| const dict = {}; | |
| if(typeof noMatch == 'function') { | |
| dict.noMatch = noMatch; | |
| } | |
| return new Proxy(() => { throw new Error('No match'); }, { | |
| set(target, property, value) { | |
| dict[property] = value; | |
| return true; | |
| }, | |
| apply(target, thisArg, args) { | |
| const value = dispatch.apply(null, args); | |
| const func = (value && dict.hasOwnProperty(value) | |
| ? dict[value] | |
| : (dict.hasOwnProperty('noMatch') | |
| ? dict['noMatch'] | |
| : target)); | |
| return func.apply(thisArg, args); | |
| } | |
| }); | |
| } | |
| // Usage: | |
| let dispatchFunc = person => person && person.manners; | |
| let noMatchFunc = () => { return 3.0; }; | |
| let coffeePrice2 = createMultimethod(dispatchFunc, noMatchFunc); | |
| coffeePrice2.polite = (person) => { | |
| return 2.00; | |
| }; | |
| coffeePrice2.rude = (person) => { | |
| return 6.00; | |
| }; | |
| let alice = { name: 'Alice', manners: 'polite' }; | |
| let bob = { name: 'Bob', manners: 'rude' }; | |
| console.log('$' + coffeePrice2(alice)); // $2 | |
| console.log('$' + coffeePrice2(bob)); // $6 | |
| console.log('$' + coffeePrice2()); // $3 | |
| coffeePrice2.veryPolite = (person) => { | |
| return 1.85; | |
| }; | |
| let carol = { name: 'Carol', manners: 'veryPolite' }; | |
| console.log('$' + coffeePrice2(carol)); // $1.85 |
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