Question

I recently read an interesting blog post on Anders Hejlsberg’s arguments against AOP.

The first anti-anti argument mentions data binding:

Myth 1. “Aspect-oriented programming is interesting for debugging and instrumentation of code and is not a full-fledged programming discipline.”

Truth 1. Anders probably stopped at the “Hello, world” example.

Although code instrumentation is certainly an important use case of AOP – and the one you would see in every “getting started” documentation – the technology significantly simplifies the work of developers when it comes to implement any non-trivial, real-life application. Just to cite a few real-life scenarios where AOP really helps:

* Data Binding (INotifyPropertyChanged) 

I’m trying to think of how AOP is used in a data binding scenario. I always assumed that binding relied on reflection to do it’s "magic." I’m pretty sure everything you need in a binding scenario is available via reflection. Is AOP being used for a (slight) performance boost?

Answer 1

It’s not the databinding he’s referring to, but the INotifyPropertyChanged (and similar) part that AOP would really shine.

Currently, when a class implements INotifyPropertyChanged, properties look like this:

private bool _isSomeProperty;
public bool IsSomeProperty
{
  get{ return _isSomeProperty;}
  set
  { 
    if( value != _isSomeProperty)
    {
      _isSomeProperty = value;
      OnNotifyPropertyChanged( "IsSomeProperty");
    }
  }
}

Where with decent AOP, they could look like this

[NotifyOnChange]    
public bool IsSomeProperty {get; set;}

Makes a big readability difference, especially when the setter for a couple properties has a few actual rules in it.

Even with generic base classes, Expressions, Reflection, and some tricky implementations, the best you hope for is:

private bool _isSomeProperty;
public bool IsSomeProperty
{
  get{ return _isSomeProperty;}
  set
  { 
    SetAndNotify( x=>x.IsSomeProperty)
  }
}

And even that’s not as readable (and is less performant as well)