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228 lines
7.9 KiB
Markdown
228 lines
7.9 KiB
Markdown
# Modelo.js [](https://travis-ci.org/kevinconway/Modelo.js)
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**A multiple inheritance utility for JavaScript.**
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## Why?
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Inheritance libraries today all seem to enforce the same clunky interface
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style. The only one of any merit these days is 'util.inherits' from the Node.js
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standard library. Only problem: no multiple inheritance.
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Wouldn't it be great if 'util.inherits' supported multiple inheritance *and*
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it stayed fast too?
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That's this library. That's why it exists.
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## util.inherits
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The 'modelo.inherits' function can act as a drop in replacement for
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'util.inherits'. Already have a code base that you want to start extending? No
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problem.
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```javascript
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var modelo = require('modelo');
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function Base() {
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// Base object constructor
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}
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Base.prototype.baseMethod = function baseMethod() {
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console.log('Method from base object.');
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}
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function Extension() {
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// Sub-object constructor
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}
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// util.inherits(Extension, Base);
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modelo.inherits(Example, Base);
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new Extension() instanceof Base; // true
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```
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## Multiple Inheritance
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Once you need to extend multiple base objects, just put more base objects in
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the call to 'inherits'.
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```javascript
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var modelo = require('modelo');
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function MixinOne() {}
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function MixinTwo() {}
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function Combined() {}
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modelo.inherits(Combined, MixinOne, MixinTwo);
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var instance = new Combined();
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instance.isInstance(Combined); // true
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instance.isInstance(MixinOne); // true
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instance.isInstance(MixinTwo); // true
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```
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Unfortunately, there is no way to make 'instanceof' work with multiple
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inheritance. To replace it, simply use the 'isInstance' method that gets added
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to your instances. It will return true for any base object in the inheritance
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tree.
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Additionally, the 'super_' attribute is still present on the new constructor in
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multiple inheritance but it only references the first prototype present in the
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call to 'inherits'. It is provided only for compatibility with `util.inherits`
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and, when using multiple inheritance, the 'super_' attribute should be avoided
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in favour of calling the target prototype directly if the form of
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`<Constructor>.prototype.<method>.call(this, ...)` or
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`<Constructor>.prototype.<method>.apply(this, ...)`.
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## You Said Something About Fast?
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All inheritance libraries have their cost. When the overhead in question affects
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the speed of object definition and creation, though, that cost must be kept
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to a minimum. Here is how this library compares to the competition:
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### Object Definition
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The typical benchmark you will see while researching inheritance tools is one
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that measures the cost of an object prototype, or class, definition followed by
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the creation of a single instance. The following results are based on a test
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which does just that. Each library produces an equivalent inheritance tree and
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spawns an instance. The full source of the benchmark can be found in
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'benchmarks/comparisons/define.js'.
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The approximate results:
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| Name | % Slower |
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----------------|-------------
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| Fiber | 0.0000 % |
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| util.inherits | 24.010 % |
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| augment | 64.601 % |
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| Modelo | 65.594 % |
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| Klass | 74.658 % |
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The [Fiber][] library is the clear winner with a 24% difference in run-time cost
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from the Node.js 'util.inherits'. Considering the implementation of
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'util.inherits' is effectively a two line wrapper around the 'Object.create'
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built-in, it's quite a surprise that Fiber is *that* much faster. Now, the
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*actual* difference between Fiber and 'util.inherits' is something on the order
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of ~0.00008 seconds which, frankly, is inconsequential.
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In fact, even the difference between Fiber and the bottom three libraries
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is inconsequential, not because the difference is not statistically
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significant but, because this benchmark only represents the time required to
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define a "class", or object prototype. This is something that happens, at most,
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once for each class, or object prototype, defined in a code base. These
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run-time costs simply do not matter unless your code base generates hundreds
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of thousands of "class" definitions.
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### Instance Creation
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A far more realistic measurement of overhead is the time it takes to create an
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instance of an object defined using an inheritance library. After all, creating
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instances necessarily happens far more often than defining the prototype:
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| Name | % Slower |
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----------------|-------------
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| Modelo | 0.0000 % |
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| util.inherits | 3.4355 % |
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| Fiber | 45.017 % |
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| augment | 48.284 % |
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| Klass | 161.79 % |
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The above results are deceptive. While it appears as though Modelo is faster
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than the others, including the Node.js 'util.inherits', the reality is that
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the run-time difference between these libraries is so small that it exceeds
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the microsecond resolution of the timer used in the benchmarks. For all intents
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and purposes there is no measurable difference between any of these libraries.
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### Conclusion
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When it comes down to it, you should pick your inheritance tool chain based on
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its interface. The run-time cost of most inheritance libraries on the market
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today is sub-microsecond and unlikely to affect the performance of your
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code.
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Note: If you find a flaw in any of the benchmarks used please open an issue on
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GitHub.
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## Setup
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### Node.js
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This package is published through NPM under the name 'modelo':
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$ npm install modelo
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Once installed, simply 'require("modelo")'.
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### Browser
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This module uses browserify to create a browser compatible module. The default
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grunt workflow for this project will generate both a full and minified browser
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script in a build directory which can be included as a ```<script>``` tag:
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<script src="modelo.browser.min.js"></script>
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The package is exposed via the global name 'modelo'.
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### Tests
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Running the ```npm test``` command will kick off the default grunt workflow. This
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will lint using jslint, run the mocha/expect tests, generate a browser module,
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and generate browser tests.
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### Benchmarks
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Running ```grunt benchmark``` will run the benchmarks discussed above. You can
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optionally install the micro-time library (```npm install microtime```) to get
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microsecond precision.
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## License
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This project is released and distributed under an MIT License.
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Copyright (C) 2012 Kevin Conway
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to
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deal in the Software without restriction, including without limitation the
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rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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sell copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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IN THE SOFTWARE.
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## Contributors
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### Style Guide
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All code must validate against JSlint.
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### Testing
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Mocha plus expect. All tests and functionality must run in Node.js and the
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browser.
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### Contributor's Agreement
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All contribution to this project are protected by the contributors agreement
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detailed in the CONTRIBUTING file. All contributors should read the file before
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contributing, but as a summary::
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You give us the rights to distribute your code and we promise to maintain
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an open source release of anything you contribute.
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[Fiber]: <https://github.com/linkedin/Fiber>
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