C#揭密II（大师们在说些什么？）
先声明这篇文章属于收藏性质的,推荐给那些喜欢dotNET技术的爱好者。
这之前我曾转载了O'Reilly的一篇关于C#的访谈录。O'Reilly一向以技术和评论公见长，他们的编辑一般都有着很深的技术背景和功力(所以出的书也比较贵haha)，所以那篇着重整个流行技术，有不少是和Java相关的；而这一篇都是MS内部的几个高手在交谈聊天，涉及的范围比上次的专访要广，里面有一些很新奇的术语和许多问题的观点。另外我认为这篇文章对以前非常熟悉COM+、ASP和Window DNA（N 层结构）的人目前评估和思考向新的dotNET体系迁移都很有帮助。
Anders Hejlsberg是个很奇怪的人，从他身上你感觉不到一个程序语言创始人那种对某种语言偏爱的狂热，却很容易感觉到他所透露出的那种对技术对程序语言的坚定和深厚理解。很喜欢他在上一篇访谈录中说的一句话：“Language is a funny thing: It's a matter of taste. Language is almost a religious thing, and it's a lifestyle choice for programmers。”不过我知道这句话说的不是他自己。这篇文章中还有好些人：Brian Harry，Peter Golde ，Scott Guthrie（ASP老怪），Mark Anders。有了这些人，Microsoft有福啊。
小气的神
2001.09.24
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Conversations _disibledevent=>
Summary: What follows is a series of conversations with Microsoft engineers, designers, and developers, looking at issues involving C#, ASP.NET, and the Common Language Runtime. (10 printed pages)
A Conversation with Anders Hejlsberg and Peter Golde _disibledevent=>Vision at Microsoft Corporation. He is the chief designer of the C# programming language and a key participant in the development of the .NET Framework. Previously, Anders was the architect for Visual J++ and the Windows Foundation Classes.
Peter Golde is a Software Design Engineer in the Developer Division at Microsoft Corporation. Peter has worked _disibledevent=>Visual Basic, Visual Basic for Applications, and Visual J++.
Q: Peter, you attended the ECMA meetings in March. Can you disclose anything about what's going _disibledevent=>word for the type system in .NET, i.e. a specification of what a class, struct, enum, or such is. CLI is really just another word for the large subset of the .NET Framework that we submitted to ECMA.
Peter Golde: The CLI includes the CLS and the CTS.
Q: Anders, after your work _disibledevent=>Delphi, Visual J++ and now C#, how do you see programming languages evolving today?
Anders Hejlsberg: Jeeez, had to ask an easy _disibledevent=>Machine (VM), and if so, what limitations or penalties associated with VMs (performance and so forth) will folks need to consider in their efforts?
Peter Golde: Yes, I think that the CLR can be considered in the broad class of things that _disibledevent=>VB) in terms of the framework?
Anders Hejlsberg: Regarding C# vs. Visual Basic, it really primarily comes down to what you already know and are comfortable with. It used to be that there was a large perf difference between VB and C++, but since C# and VB.NET use the same execution engine, you really should expect the same perf. C# may have a few more "power" features (such as unsafe code), and VB.NET may be skewed a bit more towards ease of use (e.g. late bound methods calls), but the differences are very small compared to what they were in the past.
Q: Ok, can you contrast C# with VB.NET? Questions usually come in the form of "I know you guys say VB.NET and C# let you do the same thing, but C# was designed for the CLR, so I don't believe you when you say VB.NET is just as good."
Anders Hejlsberg: Regarding C# versus VB.NET, the reality is that programmers typically have experience with either C++ or VB, and that makes either C# or VB.NET a natural choice for them. The already existing experience of a programmer far outweighs the small differences between the two languages.
Q: It has been said a few times that C# is the language designed for the CLR. Considering that all the languages that Microsoft will ship with the VS.NET will be able to target all the features of the CLR, what makes C# more CLR "friendly" than the other?
Peter Golde: I don't think that C# is necessarily any more friendly to the CLR than other languages. The CLR has been designed to be Accessible via multiple languages. However, you will probably find that C# is more strongly focused _disibledevent=>
Anders Hejlsberg: For two reference types (classes), the default Equals() method is the same as ==. But for value types (structs), there is no == operator unless you provide an implementation in the value type.
Q: Is Lock (this) similar to the synchronize key word in Java?
Peter Golde: Yes, lock (<expression>) is extremely similar to synchronized (<expression>) in Java. We don't support the notion of a modifier _disibledevent=>
Mark Anders: Note that we don't gather all of the statistics if trace==false.
Q: Could you discuss the security of the config files. I have seen a lot of concern that since they are simple XML files, they can be hacked into easily.
Scott Guthrie: We do block all access to the config files from remote users. However, I think the concern people have is whether a rogue user who gets access to the config file can modify and take over things. Note that this problem exists with ASP today as well, in that the metabase APIs can be written to, which would effectively do the same thing. However, there are some things that you can do to reduce this problem. Specifically, with ASP.NET we support the ability to "lock down" settings at a parent Directory. For example, you might want to lock down the security identity of the worker process (i.e.: the username it runs under) at the machine level and then restrict sub-applications' abilities to override it.
Q: I see confusion as to whether to mimic the Windows DNA model by creating ASP Presentation interfaces talking to COM+ components, or in the .NET era to just write code behind and stick Dynamic Link Libraries (DLLs) in the \BIN and be done with it.
Mark Anders: I would say that services provided by COM+ are still required if you want transactions. However, the model of using DCOM to put components _disibledevent=>
3. Explicitly use VBScript's "Option Explicit" keyword at the top of every ASP Page (this will become the default with ASP.NET and will also ensure that you write slightly better code today).
4. Use the "Call" keyword anytime they call a subroutine in VBScript today (for example: "Call FooBar (1, 2)"). This will enable/require them to wrap parenthesis around all subroutine arguments (if you don't use the "call" keyword, then VBScript today will raise a compilation error if you have parentheses). In VB.NET, parentheses are now required (note that the "call" keyword is still supported in VB.NET). So if they didn't use the "call" keyword, they'd have to go back and change all subroutines.
5. Avoid relying _disibledevent=>Windows 2000 a fully self-contained module for deployment purposes? In other words, does it upgrade IIS _disibledevent=>JSP. ASP.NET proves to be substantially faster than both in almost every scenario. For rich windows apps we have taken a variety of forms-based apps and have focused _disibledevent=>office, Visio, etc.?
Brian Harry: At a lower level type safe code helps reduce memory leaks, eliminates dangling pointers and deployment issues, all helping contribute to more reliable applications. We are thoroughly testing internally in every configuration we can imagine. Further, we are doing a VERY wide beta program. Recent data I saw showed that the .NET Framework Beta1 had reached almost 1 million people.
Q: What are the definite "no-no's" for developers writing to the CLR?
Brian Harry: Hmmm, most of the no-no's are the same as always—don't allocate too much memory, don't write n^2 algorithms, etc. The main things that are added, are you need to be careful where your managed/unmanaged boundaries are and how many times you cross them. You also need to be aware of security checks. Too many can kill your perf so you need to design for them.
Q: Can you comment _disibledevent=>
Brian Harry: Yes, the reason for this is that strings are immutable. This makes for a simpler programming model and eliminates problems around synchronization and sharing of strings. In some cases, it allows us to give better performance by avoiding copying strings.
StringBuilder allows you to modify the string in place. A string builder can be converted to a string and then it becomes immutable.
Q: Does this mean if I had a member variable that is a StreamReader, I will need to implement it to be able to call the StreamReader's close method?
Brian Harry: StreamReader—It will depend on how your class is used, but if you are exposing it out to arbitrary clients, then yes you might want to.
Q: Under what conditions do I need to implement Idisposable.
Brian Harry: A class should implement IDisposable if it encapsulates "limited" resources. Examples are: window handles, file handles, database connections, etc. Anything where the user of the resource needs to be able to free itpreemptively.
Q: A related question is why do you really care about resurrection, i.e. getting the object back to life once it has died?
Brian Harry: Actually, I don't care about resurrection; it is a terrible thing in my opinion. It is somewhat of a necessary evil of the notion of Finalizers. We had a plan (which we may bring back in a future version) for something called "static finalizers" that would eliminate the possibility of resurrection.
Q: Is it true that deterministic finalization cannot be achieved because of resurrection, or am I mixing them here?
Brian Harry: No, deterministic finalization has nothing to do with resurrection. Resurrection is an issue after we have already run the finalizer. Deterministic finalization (as I have most frequently heard it used) has to do with not calling the finalizer at a well-defined point in time.
Q: Which brings us back to my question about when to use long and short weak references?
Brian Harry: Long/Short—As a general rule, always use short weak references. Only use long ones if you need to access the handle to find the object even during finalization. This is a very rare need. There are some caching schemes where this turns out to be valuable but I don't think I could describe them very well without spending a while to think about it.
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