PostSharp

[cocotapioca]

Hi! I wanna do something like this:

[Singleton]
public class Something
{
    public Something()
    {
       ... initialization ...
    }
... blah blah ...
}

And when i wrote "new Something()" always get the same instance.
Is this possible? Im thinking on doing a replacement of the .ctor il to get the same instance, stored in a static field created in post compilation. Or trying to do it with Laos is possible or easier?

[cocotapioca]

After some time taking exams and on vacation i wanna continue with this singleton attribute. How can i add a new field (static) to a Type? There is some example a TypeAdvice? I need to treat constructors like methods (actually they are, but are called with newobject)?
Ill appreciate any help

[gfraiteur]

Actually, every time you add an aspect to a type (or a field or method of a type), you add a static field to this type: the aspect itself.

Therefore, every instance field of an aspect can be considered as a static field of the declaring type.

If you don't need to "remember" the value of that field between compile- and run-time, you should mark the field as [NonSerialized].

It is not currently possible to intercept calls to constructors, so I don't see how you could implement the Singleton pattern.

Gael

[cocotapioca]

Ok, thanks for the reply, but how oyu use the JointPointind.InsteadOfNewObject?

Im thinking of doing something like this:
*mark the singleton type
*create a Intance getter and a field to store the sole instance
*scan all methods/constructors for the use of newobject+ctor for singleton types
*replace that by a call to get_Instance

[gfraiteur]

Ok, thanks for the reply, but how oyu use the JointPointind.InsteadOfNewObject?

It is available only from PostSharp Core, not from PostSharp Laos. So you should write your own abstract aspect.

[cocotapioca]

Yes im using Postsharp.core directly, not laos. So you say i need to write my own abstract aspect, i assume that ther is not example about that. Ill dive into postsharp code.
When you use JointPointKind.InsteadOfNewObject? Is a Type o Method kind of joint point?
Have you use this feature? Can you show me some code?

Thanks for the quick reply.

[gfraiteur]

It is a method-level advice. You should specify the constructors to intercept in the operand, and null (=all methods) for the set of targets.

There is an example of how to create an aspect based on Laos: PostSharp.Samples.Librarian.

Good luck - you will have good time .

[cocotapioca]

Thanks for the reply.
I have a question, how do i get a MetadataDeclaration for the constructor .ctor from TypeDefDeclaration?

[gfraiteur]

Something like;

typeDef.Methods.GetByName(".ctor")

Gel

[cocotapioca]

That was my first try but typeDef.Methods.GetByName return an IEnumerable<MethodDefDelcaration> and operands is a IEnumarable<MetadataDeclaration>
And cant be casted.

Cheers.
Ignacio