The concept of proxy methods will become an important, core concept in ease.js
that will provide strong benefits for creating decorators and proxies, removing
boilerplate code and providing useful metadata to the system. Consider the
following example:
Class( 'Foo',
{
// ...
'public performOperation': function( bar )
{
this._doSomethingWith( bar );
return this;
},
} );
Class( 'FooDecorator',
{
'private _foo': null,
// ...
'public performOperation': function( bar )
{
return this._foo.performOperation( bar );
},
} );
In the above example, `FooDecorator` is a decorator for `Foo`. Assume that the
`getValueOf()` method is undecorated and simply needs to be proxied to its
component --- an instance of `Foo`. (It is not uncommon that a decorator, proxy,
or related class will alter certain functionality while leaving much of it
unchanged.) In order to do so, we can use this generic, boilerplate code
return this.obj.func.apply( this.obj, arguments );
which would need to be repeated again and again for *each method that needs to
be proxied*. We also have another problem --- `Foo.getValueOf()` returns
*itself*, which `FooDecorator` *also* returns. This breaks encapsulation, so we
instead need to return ourself:
'public performOperation': function( bar )
{
this._foo.performOperation( bar );
return this;
},
Our boilerplate code then becomes:
var ret = this.obj.func.apply( this.obj, arguments );
return ( ret === this.obj )
? this
: ret;
Alternatively, we could use the `proxy' keyword:
Class( 'FooDecorator2',
{
'private _foo': null,
// ...
'public proxy performOperation': '_foo',
} );
`FooDecorator2.getValueOf()` and `FooDecorator.getValueOf()` both perform the
exact same task --- proxy the entire call to another object and return its
result, unless the result is the component, in which case the decorator itself
is returned.
Proxies, as of this commit, accomplish the following:
- All arguments are forwarded to the destination
- The return value is forwarded to the caller
- If the destination returns a reference to itself, it will be replaced with
a reference to the caller's context (`this`).
- If the call is expected to fail, either because the destination is not an
object or because the requested method is not a function, a useful error
will be immediately thrown (rather than the potentially cryptic one that
would otherwise result, requiring analysis of the stack trace).
N.B. As of this commit, static proxies do not yet function properly.
Finally feels like things are starting to come together.
It's rather interesting looking back. Each time I begin writing a piece of
software, I think to myself, "This is the best way to do it." Well, generally.
Perhaps the implementation could have been better, but I may not have had the
time. However, the general concept remains.
Each time I look back months later and find that I disagree with certain
decisions. I find certain implementations to be messy or poorly constructed. Or
perhaps I was just being lazy to begin with. Whatever the case, it is
comforting. It shows that one is continuing to learn and evolve.
Now, in the case of ease.js, we're working with a number of different factors in
regards to my perception of prior code quality. Primarily, I'm looking at a
basic implementation (in this case, I'm referring to test cases) that served as
a foundation that could be later evolved. I didn't have the time to devote to a
stronger solution. However, since the project has evolved so far past my
original expectations, a more sophisticated solution is needed in order to
simplify the overall design. That is what happened here.
Of course, we're also looking at a year's worth of additional, intimate
experience with a language.
Regardless of the reason, I love to see software evolve. Especially my own. It's
as if I'm watching my child grow. From that, I can get a great deal of
satisfaction.
One shouldn't expect perfection. But one should certainly aim for it.
Mike Gerwitz