PostSharp - args.ReturnValye = default(T) -> T = method return type, how? - return-type

Question

My aspect:
[Serializable]
class FlowController : OnMethodBoundaryAspect
{
[ThreadStatic]
private static bool logging;
public override void OnEntry(MethodExecutionArgs args)
{
if (logging)
return;
try
{
logging = true;
if (ProgramState.State() == false)
{
args.ReturnValue = ""; // WHAT DO I SET HERE?
args.FlowBehavior = FlowBehavior.Return;
}
}
finally
{
logging = false;
}
}
}
Basically the ProgramState.State() method checks if the program is running(true),paused(loops while isPaused == true), stopped(false), this should control the if methods can run or not(basically a start pause/resume stop thing)
But sometimes i get nullreferences when returning from the method.
i am interested in knowing how can i set the return type to the default return type of the method.

Answer 1

It is tested with PostSharp 6.0.29
Before use it please check required null controls.
If method is async Task
public override void OnException(MethodExecutionArgs args)
{
var methodReturnType = ((System.Reflection.MethodInfo)args.Method).ReturnType;
var runtime = methodReturnType.GetRuntimeFields().FirstOrDefault(f => f.Name.Equals("m_result"));
//Only if return type has parameterless constructture (should be check before create)
var returnValue = Activator.CreateInstance(runtime.FieldType);
args.ReturnValue = returnValue;
}
And if method is not async
public override void OnException(MethodExecutionArgs args)
{
var methodReturnType = ((System.Reflection.MethodInfo)args.Method).ReturnType;
//Only if return type has parameterless constructture (should be check before create)
var returnValue = Activator.CreateInstance(methodReturnType);
args.ReturnValue = returnValue;
}

Answer 2

You can make your aspect class generic with the generic parameter representing the method return type. Then you need to create a method-level attribute that is also an aspect provider. The attribute will be applied to the user code and in turn it can provide the correct instance of the generic aspect.
[Serializable]
[MulticastAttributeUsage( MulticastTargets.Method )]
public class FlowControllerAttribute : MethodLevelAspect, IAspectProvider
{
public IEnumerable<AspectInstance> ProvideAspects(object targetElement)
{
MethodInfo method = (MethodInfo) targetElement;
Type returnType = method.ReturnType == typeof(void)
? typeof(object)
: method.ReturnType;
IAspect aspect = (IAspect) Activator.CreateInstance(typeof(FlowControllerAspect<>).MakeGenericType(returnType));
yield return new AspectInstance(targetElement, aspect);
}
}
[Serializable]
public class FlowControllerAspect<T> : IOnMethodBoundaryAspect
{
public void RuntimeInitialize(MethodBase method)
{
}
public void OnEntry(MethodExecutionArgs args)
{
args.ReturnValue = default(T);
args.FlowBehavior = FlowBehavior.Return;
}
public void OnExit(MethodExecutionArgs args)
{
}
public void OnSuccess(MethodExecutionArgs args)
{
}
public void OnException(MethodExecutionArgs args)
{
}
}
// Usage:
[FlowController]
public int Method()
{
// ...
}