Wednesday, April 2, 2008

On Accessors and Mutators

I was just exploring the Google Visualization API reference and found myself a little hung up something. It's not just Google's API, but they are certainly a huge propagator of code. It's not the first time I've been hung up on this, either. The problem is that most APIs that use the Accessor/Mutator pattern follow it in the same, and in my opinion wrong, way. What is the point of declaring and implementing a unique function - no - two functions for every property contained by an Object? In fact why do we need any more than exactly two functions total to get or set any property or, in fact, any Object?


Why not just get(namedAttribute) and set(namedAttribute, value)?

set("numberOfRows", 6);

Realize that 6 is probably not the literal integer 6, but rather an Object itself or perhaps a Collection (of size 1) containing literal, primitively typed values. But that is hardly of consequence in the scheme of things, it seems to me. I dread even having to make the case for efficiency. Programmers still get hung up on efficiency too much in terms of cycles and RAM. While I am sensitive to these concerns (for reasons of achieving enough throughput to support fluid user interaction) such concerns pale in comparison to what is lost overall to complexity of integration. How many API's do we want to learn, really? Domain-specific languages are much easier to learn and use, and more so when there aren't too many competing DSLs floating around a domain.

Perhaps I have it wrong and it is all a trivial point I am making. But it seems an awful waste of time doing it the other way. What kind of code bloat is being propagated? What happens when you add a new attribute? In fact, the ability to declare an arbitrary property and assign it to any Object is a powerful mechanism in software. It will be used and abused one way or the other so we should anticipate and handle it. But specifically, this kind of abstract polymorphism is ideal for serialization and deserialization of database records without having to tightly bind classes to database constructs through object relational mapping. Whether using XML, standard object notation, or standard delimited formats, there are multiple ways to deserialize any Object into memory for use by business logic without having to declare and implement a class for the Object.

In fact, one interface for get and one for set is much more flexible on the whole. Integration and interoperability with other programs is much easier with a single get/set. The ability for interoperating software programs to bind solely to a universal input/output protocol, and for interoperating software to remain blissfully unconcerned with the inner workings of peers is beyond powerful. Then we can focus on the functional roles of software. What does it do? I don't care how (beyond the I/O interface)(and I do care how well). When you get to that point, software can program other software (within a security model, of course). This kind of integration is also easier to maintain. Consider an implementation that uses XML as the carrier. The main Do-Until-Error loop is as simple as: While(Element is recognized) Process Element; Else Throw/Ignore (Unrecognized Element Error). A secondary error condition will exist in the event that expected inputs are no longer generated as outputs from peers*. In both cases, the situations are reduced to a matter of choosing how to process output from peers as it is provided and not also a matter of refactoring the interface between peers. It's all the UNIX command line applied to the Web. And I am certainly not the first or only person to have noticed.

* A third condition occurs when input is malformed

No comments: