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<div style='display: inline'> <h1 style='font-family: Malgun Gothic, Consolas; font-size: 20pt; color: #006699; text-align: center; font-weight: bold'>C#에서 사용자 정의 예약어가 가능할까요?</h1> <p> 마침, 최근 C# 개발자들 사이에서 이런 토론이 있었습니다.<br /> <br /> <pre style='height: 400px; margin: 10px 0px 10px 10px; padding: 10px 0px 10px 10px; background-color: #fbedbb; overflow: auto; font-family: Consolas, Verdana;' > <span style='color: blue; font-weight: bold'>Subject: User defined keywords.</span> Date: Tue, 15 Apr 2014 23:27:20 -0400 I see that now with Roslyn people are having lots of ideas. But I actually don't plan to release my own compiler based on Roslyn, I would really like to improve C# and .NET in general. A thing that I really miss in C# (and in all languages that I use) is the possibility for the users to create their own "keywords"/control flow structures. I will try to explain with an example. Imagine this code: abortsafeusing(var someResource = new ResourceThatShouldNotBeAborted()) { someResource.DoSomething(); } It could be translated into this: { ResourceThatShouldNotBeAborted someResource = null; try { try { } finally { // code inside a finally will never be aborted. someResource = new ResourceThatShouldNotBeAborted(); } // an abort while executing DoSomething is not the problem. // the resource acquisition and the dispose must be guaranteed. someResource.DoSomething(); } finally { if (someResource != null) someResource.Dispose(); } } What I am saying here is not that I want the C# team to add the abortsafeusing. I know that abort is bad and this is not the point. The point is: What if the language allowed me to create such "keyword"? Or, of course, any other I see fit? Note that using delegates doesn't give the same effect. A delegate can't do an yield return for the main body of a method, while a code inside a using body can (and, if these user keywords were supported, it will be possible too). How could this be done? By methods decorated with some specific attribute. By classes/structs that implement a specific interface. Imagine that the abortsafeusing was implemented by a class like this: [UserKeyword(name="abortsafeusing")] public sealed class AbortSafeUsing<T>: UserBlockKeywordThatDeclaresAVariable<T> where T: IDisposable { private T _objectToDispose; protected override void BlockEnter(Func<T> value) { try { } finally { _objectToDispose = value(); } } // The exception is null when the block ends normally, but contains // the exception if it ends forcibly. protected override void BlockExit(Exception exception) { if (_objectToDispose != null) _objectToDispose.Dispose(); } } I understand that without analyzing the IL the final code will actually include a creation of an instance of the AbortSafeUsing class. Yet, as a user, I will be able to add a new "keyword" to the language. By allowing the "user keywords" to be combined we could simulate user made ifs, elses, switches and others. This could actually simplify a lot of places that are using delegates today, will behave more normally (as a return inside one of those user made blocks will return the actual method, not the delegate method) and will not be limited to a single action. We can say that if we had that support from the start that the using, the foreach and the lock keywords could be "user made" keywords. And, of course, if the .NET itself could "inline" the code inside the BlockEnter/BlockExit calls and avoid the construction of the class it would be even better. My idea is that such keywords need to be imported, maybe the same way we do with the using to import namespaces (and that's now expanded to support classes). So, what do you think? I personally see a lot of potential to create "declarative like" APIs that are actually built in real C# code. </pre> <br /> 위의 내용을 한마디로 정리하면 C#에서 사용자 정의 예약어를 갖고 싶다는 것입니다. Roslyn이 서서히 알려지면서 일부 C# 개발자들이 그동안 기다리던 사용자 정의 예약어에 대한 구현 가능성을 타진해 본 것입니다.<br /> <br /> 그런데... 이에 대한 "Anders Hejlsberg"의 대답이 나왔습니다.<br /> <br /> <div style='BACKGROUND-COLOR: #ccffcc; padding: 10px 10px 5px 10px; MARGIN: 0px 10px 10px 10px; FONT-FAMILY: Malgun Gothic, Consolas, Verdana; COLOR: #005555'> Lucian, you wrote:<br /> Anders’ answer to this is basically that .NET already has a language that’s fantastic for letting you create your own DSL inside of it. That language is F#. He doesn’t want it to be C#.<br /> </div><br /> <br /> 결국 "No"로 끝나는 군요. ^^<br /> <br /> 물론, C# 컴파일러가 이제 Roslyn으로 바뀌면서 소스코드가 모두 공개되어 사용자 정의 예약어를 만들수는 있겠지만, 언어적인 차원에서의 예약어를 쉽게 만드는 것은 일단 기대를 안하는 것이 좋을 것 같습니다.<br /> </p><br /> <br /><hr /><span style='color: Maroon'>[이 글에 대해서 여러분들과 의견을 공유하고 싶습니다. 틀리거나 미흡한 부분 또는 의문 사항이 있으시면 언제든 댓글 남겨주십시오.]</span> </div>
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