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springaopaspectjpostsharp
Matthias
Matthias

Reputation: 16209

Are typed/generic aspects worth the effort?

I've done a little research on typed/generic aspects. An important fact about aspects is obliviousness. So the concerns of the aspects should be orthogonal to the domain concerns. Nevertheless there are investigations to make AspectJ type safe (StrongAspectJ) / introduce per-type aspects using generics. One paper mentioned an implementation of the Flyweight pattern as an aspect. Now I'm wondering if there are more use cases for generic aspects?

Upvotes: 3

Views: 614

Answers (2)

Gael Fraiteur
Gael Fraiteur

Reputation: 6857

PostSharp is weakly typed, i.e. the advices see arguments and return values as 'objects'. There is some support for generic aspects in PostSharp (aspects can be generic classes), but it is not very useful since the advises are weakly typed.

Note that behind the cover, the glue code generated by PostSharp is strongly typed. But everything is downcast to an object when exposed to aspect code.

I'm considering implementing strongly-typed advised in a next version of PostSharp, possible with support of generic arguments. The reason would be run-time performance, because boxing of value types into an object brings a considerable performance overhead. Note that generics are implemented differently in .NET than in Java, so the point may need to be discussed differently on both platforms.

Feel free to contact me personally if you need any help for your thesis.

Upvotes: 2

John Watts
John Watts

Reputation: 8885

Auto-generating some of the boilerplate to make a class callable via RMI is another use case. That example implements some around advice for a bunch of methods.

pointcut callsToServer(Type T):
    call(public T Server.*(..)) && this(Client)
T around(Type T): callsToServer(T) {
    T obj = null;
    try {
        obj = proceed();
    } catch (java.rmi.RemoteException ex) {}
    return obj;
}

Generics allow you to say "we are going to return an object of the same type the method signature says". This is true, of course, if we just return the object. We might be able to do something similar with "after throwing" advice, but we wouldn't be able to manipulate the return value to translate a RemoteException into a null return value.

Upvotes: 1

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