Why did the BeforeFieldInit behavior change in .NET 4?

Question

In C# 4, the behavior of types without the beforefieldinit flag was changed, so now a type initializer can call before first use of any static field of the class.

My questions are why has the C#/.NET team changed that behavior? What is the main reason? Can you show any practical example where this change makes any sense?

Hoffarth

Reference? Where did you read this? – Grayce

I read it here: link And in my oppinion the main reason is perfomance of extension methods? What do you think? – Hoffarth

Irrelevant. These things are undocumented for a reason. – Heller

Answer 1

The behaviour has always been within the bounds of what's documented - it's just that it changed from being eager to lazy in .NET 4.

I suspect the JIT team managed to find a way to make it lazy without a performance penalty... or possibly it helps performance somewhere else. This is likely to only be one such change in behaviour within the .NET 4 CLR vs the .NET 2 CLR... it happens that I noticed it, but I doubt that many other people did. I think it's entirely reasonable for the JIT team to adjust things as they see fit, within the documented guarantees.

Ultimately, if this makes your code fail, you've got a bug already.

Proliferous

Thank for your answer! Do you know how JIT compiler call type initialazers? Its compiles a method with call of a type initialazer twice or not? I mead that before first call I have a perfomance lack while method executes, but second call of the methods has normal perfomance. – Hoffarth

@Smeliy: I don't know, to be honest. I would expect there to be some sort of thunking going on, but I've always left the details to the JIT team :) – Proliferous