I am looking at adding logic to a library I am working on that would require the need for a Dynamic Proxy. I would like to get some advice from user\'s who have used these
I am a committer to Castle, contributing to Dynamic Proxy, so I may be biased, but I generally think Castle's Dynamic proxy is far better solution. I'm talking here about LinFu DynamicProxy v1.0 because that's what I'm familiar with. LinFu.Proxy 2 is based on Mono.Cecil and is rewritten from the scratch.
invocation.Proceed();
for LinFu, it looks like this (actual method/property name may vary as I'm writing it from memory)
//invocation.TargetMethod is MethodInfo, so you're using reflection
invocation.TargetMethod.Invoke(invocation.Target,invocation.Parameters);
The performance issue, mentioned by the other answer are not DynamicProxy issue, but are result of bug in Microsoft's implementation of BCL (on Mono there is no such issue BTW). This only manifests itself when you have many (over 200+) proxy types in single ModuleScope.
Solution is trivial - don't generate that many proxy types (usually you won't have to) or use many ModuleScopes/ProxyGenerators (for example Rhino.Mocks uses this approach)
Personally I do not develop on Mono, so I don't have firsthand experience, however there are libraries using Castle DP on Mono, and we didn't get any compliaints so i guess it works just fine.
Since my benchmark few months ago, there has been no new release of Castle DP (new version is targeted at the end of the year). LiFu has a 2.0 version, but I'm not sure if it is trunk only, or released. I don't know about Spring or Unity.