The other day it occurred to me while I was browsing the API that the interceptor interface could have been implemented as a series of events on the Session/SessionFactory. Events were added to C# to help avoid the problem of coarse-grained interfaces. For instance, if I only want to listen to the OnLoad message I must implement handlers for several other events. This means that several empty functions are called on each object I retrieve from the database. This performance impact may seem negligible to some, but it is conceivable that it may be an unacceptable cost for certain projects.

It seems that certain API differences have been introduced to make NHibernate were idiomatic of the dot net framework (Enumerable vs. Iterate, etc). Might this be a worthwhile change in the future (some future version perhaps)?

While there could be architecture-related reasons to switch from IInterceptor to .NET events, it's completely pointless to think about performance here. Call of an empty method costs nearly nothing. At the same time, call via a delegate is a bit slower than direct call of an interface's method. Most likely the performance gain of not calling empty methods will be less than the loss from using delegates.

NHibernate 1.0 is/will be the port of Hibernate 2.1 which don't use events.

We will think about adding .NET-specific/new features after its release.