Introducing cip Classical Inheritance Pattern at its best
mixin() and does not compromise on any of the principals of the pseudo-classical inheritance pattern, none at all.
Cip is a big step towards bundling the Classical pattern wholesale and offering a compact, robust and small library that will help us apply sophisticated inheritance patterns throughout our projects.
Update 17 Feb 2014, The library was originally named
inher, didn’t like it, changed to
The Pseudo-Classical Pattern
There are many variants of Pseudo-Classical pattern implementations, we won’t get into the fine grained details of how it actually happens, it will suffice to demonstrate how the pattern is applied in the Node.js environment, using the language library
So that’s the pattern in a nutshell, that’s too much boilerplate to apply the inheritance pattern, we have to require the
util library, we have to properly invoke the parent constructor (minding the right amount of arguments passed), and then apply the actual inheritance using
util.inherits(). What if we could pack all these operations in a single function? Meet Cip.
Working with Cip
Cip’s first class citizen is the
extend() method. It will perform the same exact operations as pseudo-classical and apply the inheritance pattern with just a one liner. Here’s how the same example would be authored using Cip.
You notice that the result is exactly the same, we tossed the
util library and the
inherits() declaration, and we tossed the Parent Constructor invocation in the
ChildBase constructor. Passed arguments also work as expected and populate throughout the inheritance chain.
What extend() does
extend() function is a Static function assigned directly on the Constructor. When invoked it will create a new Constructor that encapsulates your provided constructor, or use a noop if none is defined. After applying the Classical Inheritance Pattern,
extend() will copy all the inheritance Static functions to the new constructor so itself will be able to perform
extend() and all the other functions we’ll see in a very while.
This enables you to perform infinite inheritance using the tools provided, this is a valid statement:
Mixing in different Constructors
Mixins, the forbidden fruit. Mixins enables us to borrow the prototypal methods of another Constructor and use them as our own in our Constructor. To create a mixin using the tools at hand (node’s
util library) one would have to do this, copying the example above:
You can see how the plot thickens here, hopefully Cip has you covered and provides a convenience method that performs the same exact operations. Meet
mixin() method accepts any number of arguments, as long as they are of type Function, or an Array of Functions, all representing Constructors.
Mixins have never been easier to apply. One might wonder what happens with the arguments the Constructors expect, and you will be right on the money, passing arguments down the inheritance chain is one of the tedious tasks you have to perform, taking care what argument is passed to what constructor. Cip abstracts that away from you and provides every constructor, either it be a Parent or a Mixin, with the same arguments that were passed on instantiation.
2 will get passed on to the Parent Constructor (
Base) and all the parents there might be, and every Mixin we defined (MixinOne, MixinTwo…) and all their respective parents! So you have to mindful of how many arguments your Constructor accepts, or in other words, the arity.
Now not all is lost! Cip gotz your back one more time, introducing the Stubbed Arguments!
Argument Stubbing is providing arguments to the
extend() function with the intend of passing them to the Parent constructor. Consider this case:
Argument Stubbing can be infinitely nested and inherited, Inher keeps track of each Constructor’s Stubbed Arguments and applies them no matter how long the inheritance chain is. The same principle applies to Constructors that were used as Mixins. Aint this cool? Stubbed Arguments can also be composed over multiple ancestors, check this out:
Working with Singletons
A Singleton is a single instance of a constructor, that is used in every occasion throughout the application’s lifetime. The singleton pattern requires a method for easily fetching that single instance and dictates a few other details that are beyond our scope here. Singletons are particularly useful for core components of our Application, Models, Controllers, Views, Routers, these are components that we need to instantiate once per runtime. Cip will create a Singleton Constructor with
extendSingleton(). This explicit statement allows for better clarity and will hopefully save you from some common pitfalls.
No matter where in the code we invoke
UserModel.getInstance() we will always get the same exact instance. If you are using Static methods and properties on your constructor, like an enumeration you will find this pattern of requiring particularly useful:
Notice the use of the
UserModel.Type, that’s an enum defined statically on the UserModel constructor.
How Cip plays nice with everyone
So far so good, but as you might have suspected, the inheritance chain always ends at the Cip’s base class. That’s not required. Using the
cast() method you can augment any vanilla constructor with Cip’s properties and functions:
Ta-dahhhh! Now all your ancestors will inherit the EventEmitter properties and methods. Plain simple, effective, works.
Hope you like it, let me know if you find it useful.blog comments powered by Disqus