While I've been doing a bunch of .NET development over the last year, I haven't really developed any class libraries until now (been web services and web application stuff, mostly). Being a good .NET citizen, I set the CLSCompliant attribute. I was coding merrily along, using the C# coding standard that I've adopted - camel case for members, Pascal case for properties and methods. Everything was ducky until I tried to add a protected field and a corresponding public accessor property. The compiler complained that this wasn't CLS compliant, since case-insensitive languages like VB.NET can't differentiate between the starts-with-lower-case field and the corresponding starts-with-upper-case property. Doh! Not sure why I never thought of that. The .NET framework style guide recommends camel case for protected fields, but I guess they didn't consider the case where there's a corresponding public property when they wrote that recommendation.
My first thought was to switch to the other common style that I've seen (but that I've never been crazy about) - prefixing fields with an underscore. No love - that's also not CLS compliant. My next thought was - what does Microsoft do in the framework classes? I poked around the Rotor source code site, trying to find an example. Guess what? Couldn't find one. The only protected members that I found were either internal or had no corresponding public property. The majority of the fields that I looked at were simply declared as private with a public accessor property.
Now, this was hardly a comprehensive search - I just picked several files at pseudo-random (trying to pick files that would have reasonably substantial code in them). I haven't downloaded the full Rotor source and searched. But that said, I thought it was kind of interesting that there wasn't a single example to be found. The style guide says that a protected instance field is "rarely used", and I get that. The only reason I can envision using one is in performance sensitive code where you don't want a deriving class to incur the overhead of a property accessor. Pretty obscure. So I'm going to stick with the private field, public/protected property model.
As a final note, in poking around the Rotor source it seems that the Microsoft developers mostly used three different coding styles for fields - camel casing, leading underscore, and the old Hungarian style "m_". I wonder if they've settled on one style going forward.
I also wonder if I should just get a life and stop spending so much time thinking (and blogging) about stuff like this.