這些技術的出現為什么驚世駭俗，打個比方，就好比是一塊大家都認為已經熟悉無比，再無秘密可言的土地上，忽然某天有人挖到原來地下還蘊藏著最豐富的石油。在這之前的C++雖然也有一些細節，但也還算輕易把握，那可是C++程序員們的happy old times，因為C++的一切都一覽無余，everything is figured out。然而《Modern C++ Design》的出世告訴人們，“瞧，還有多少細節你們沒有把握啊?！庇谑荂++程序員們久違的激情被重燃起來，奮不顧身的踏入細節的沼澤中。尤其是，模板編程將C++的細節進一步挖掘到了極致——我們干嘛關心涉及類對象的隱式轉換的優先級高低?看看boost::is_base_of就可以知道有多詭異了。
但最大的問題還在于，對于這些細節的關注還真有它合適的理由：我們要開發現代模板庫，要開發active library，就必須動用模板編程技術，要動用模板編程技術，就必須利用語言的犄角旮旯，enable_if，type_traits，甚至連早就古井無波的C宏也在亂世中重生，看看boost::preprocessor有多詭異就知道了，連C宏的圖靈完備性(預編譯期的)都被挖掘出來了。為什么要做這些?好玩?標榜?都不是，開發庫的實際需求。但這也正是最大的悲哀了。在boost里面因實際需求而動用語言細節最終居然能神奇的完成任務的最好教材就是boost::foreach，這個小設施對語言細節的發掘達到了驚天地泣鬼神的地步，不信你先試著自己去看看它的源代碼，再看看作者介紹它的文章吧。而boost::typeof也不甘其后——C++語言里面有太多被“發現”而不是被“發明”的技術。難道最初無意設置這些語言規則的家伙們都是Oracles? 因為沒有variadic templates，人們用宏加上缺省模板參數來實現類似效果。因為沒有concepts，人們用模板加上析構函數的細節來完成類似工作。因為沒有typeof，人們用模板元編程和宏加上無盡的細節來實現目標… C++開發者們的DIY精神不可謂不強?！ ∪欢?，假如僅僅是因為要開發優秀的庫，那么涉及這些細節都還是情有可原的，至少在C++09出現并且編譯器廠商跟上之前，這些都還能說是不得已而為之。但我們廣大的C++程序員呢?大眾是輕易被誤導的，我也曾經是。以為把握了更多的語言細節就更牛，但實際卻是那些語言細節十有八九是平時編程用都用不到的。C++中眾多的細節雖然在庫設計者手里面有其用武之地，但普通程序員則根本無需過多關注，尤其是沒有實際動機的關注。一般性的編碼實踐準則，以及基本的編程能力和基本功，乃至基本的程序設計理論以及算法設計。才是真正需要花時間把握的東西?！ W習最佳編碼實踐比學習C++更重要?？磧炐愕拇a也比埋頭用差勁的編碼方式寫垃圾代碼要有效。直接、清楚、明了、KISS地表達意圖比玩編碼花招要重要… 避免去過問任何語言細節，除非必要。這個必要是指在實際編程當中碰到問題，這樣就算需要過問細節，也是最省事的，懶惰者原則嘛。一個把握了基本的編程理念并有較強學習能力的程序員在用一門生疏的語言編程時就算拿著那本語言的圣經從索引翻起也可以編出合格的程序來。十年學會編程不是指對每門語言都得十年，那一輩子才能學幾門語言哪，假如按字母順序學的話一輩子都別指望學到Ruby了;十年學習編程更不是指先把語言特性從粗到細全都吃透才敢下手編程，在實踐中提高才是最重要的?！ ≈劣谶@種摳語言細節的哲學為何能在社群里面呈野火燎原之勢，就是一個心理學的問題了。想像人們在論壇上討論問題時，一個對語言把握很細致的人肯定能夠得到更多的佩服，而由于論壇上的問題大多是小問題，所以解決實際問題的真正能力并不能得到顯現，也就是說，知識型的人能夠得到更多佩服，后者便成為動力和仿效的砝碼。然而真正的編程能力是與語言細節沒關系的，熟練運用一門語言能夠幫你最佳表達你的意圖，但熟練運用一門語言絕不意味著要把它的邊邊角角全都記住。懂得一些常識，有了編程的基本直覺，碰到一些細節錯誤的時候再去查書，是最節省時間的辦法?！ ++的書，Bjarne的圣經《The C++ Programming Language》是高屋建瓴的?！洞笠幠++程序設計》是挺務實的?！禔ccelerated C++》是最佳入門的?！禖++ Templates》是僅作參考的?！禖++ Template Metaprogramming》是精力過剩者可以玩一玩的，普通程序員碰都別碰的。《ISO.IEC C++ Standard 14882》不是拿來讀的。Bjarne最近在做C++的教育，新書是絕對可以期待的。 P.S. 關于如何學習編程，g9的blog上有許多出色的文章：這里，這里，這里，這里… 實際上，我建議你去把g9老大的blog翻個底朝天 :P 再P.S. 書單?我是遑于給出一個類似《C++初學者必讀》這種書單的。C++的書不計其數，被公認的好書也不勝枚舉。只不過有些書輕易給初學者造成一種錯覺，就是“學習C++就應該是這個樣子的”。比如有朋友提到的《高質量C/C++編程》，這本書有價值，但不適合初學者，初學者讀這樣的書輕易一葉障目不見泰山。實際上，正確的態度是，細節是必要的。但細節是次要的。其實學習編程我覺得應該最先學習如何用偽碼表達思想呢，君不見《IntrodUCtion to Algorithm》里面的代碼?《TAOCP》中的代碼?哦，對了它們是自己建立的語言，但這種僅教學目的的語言的目的就是為了避免讓寫程序的人一開始就忘了寫程序是為了完成功能，以為寫程序就是和語言細節作斗爭了。Bjarne說程序的正確性最重要，boost的編碼標準里面也將正確性列在性能前面?！ 〈送猓坏┙⒘苏_的學習編程的理念，其實什么書(只要不是太垃圾的)都有些用處。都當成參考書，用的時候從目錄或索引翻，基本就對了?！ ≡僭貾.S. myan老大和g9老大都給出了許多出色的見解。我不得不再加上一個P.S。具體我就不摘錄了，假如你讀到這里，請務必往下看他們的評論。轉載者別忘了轉載他們的評論:-) 許多朋友都問我同一個問題，到底要不要學習C++。其實這個問題問得很沒有意義。“學C++”和“不學C++”這個二分法是沒意義的，為什么?因為這個問題很表面，甚至很浮躁。重要的不是你把握的語言，而是你把握的能力，借用myan老大的話，“重要的是這個磨練過程，而不是結果，要的是你粗壯的腿，而不是你身上背的那袋鹽巴?！?。此外學習C++的意義其實真的是醉翁之意不在酒，像C/C++這種系統級語言，在學習的過程中必須要涉及到一些底層知識，如內存治理、編譯連接系統、匯編語言、硬件體系結構等等等等知識(注重，這不包括過分犄角旮旯的語言枝節)。這些東西也就是所謂的內功了(其實最最重要的內功還是長期學習所磨練出來的自學能力)。對此大嘴Joel在《Joel On Software》里面提到的漏洞抽象定律闡述得就非常漂亮?！ ∷裕鸢甘?，讓你成為高手的并不是你把握什么語言，精通C++未必就能讓你成為高手，不精通C++也未必就能讓你成為低手。我想大家都不會懷疑g9老大假如要抄起C++做一個項目的話會比大多數自認熟練C++的人要做得漂亮。所以要害的不是語言這個表層的東西，而是底下的本質矛盾。當然，不是說那就什么語言都不要學了，按照一種曹操的邏輯，“天下語言，唯imperative與declarative耳”。C++是前者里面最復雜的一種，支持最廣泛的編程范式。借用當初數學系入學大會上一個老師的話，“你數學都學了，還有什么不能學的呢?”。學語言是一個途徑，假如你把它用來磨練自己，可以。假如你把它用來作為學習系統底層知識的鑰匙，可以。假如你把它用來作為學習如何編寫優秀的代碼，如何組織大型的程序，如何進行抽象設計，可以。假如掉書袋，光啃細節，我認為不可以(除非你必須要用到細節，像boost庫的coder們)。 然后再借用一下g9老大的《銀彈和我們的職業》中的話： 銀彈和我們的職業發展有什么相干?很簡單：我們得把時間用于學習解決本質困難。新技術給高手帶來方便。菜鳥們卻不用指望被新技術拯救。沿用以前的比喻， 一流的攝影師不會因為相機的更新換代而丟掉飯碗，反而可能借助先進技術留下傳世佳作。因為攝影的本質困難，還是攝影師的藝術感覺。熱門技術也就等于相機。 不停追新，學習這個框架，那個軟件，好比成天鉆研不同相機的說明書。而熱門技術后的來龍去脈，才好比攝影技術。為什么推出這個框架?它解決了什么其它框架 不能解決的問題?它在哪里適用?它在哪里不適用?它用了什么新的設計?它改進了哪些舊的設計?Why is forever. 和 朋友聊天時提到Steve McConnell的《Professional Software Development》里面引了一個調查，說軟件開發技術的半衰期20年。也就是說20年后我們現在知識里一半的東西過時。相當不壞。朋友打趣道：“應 該說20年后IT界一半的技術過時，我們學的過時技術遠遠超過這個比例。具體到某人，很可能5年他就廢了”。話雖悲觀，但可見選擇學習內容的重要性。學習 本質技藝(技術遲早過時，技藝卻常用長新)還有一好處，就是不用看著自己心愛的技術受到挑戰的時候干嚎。C/C++過時就過時了唄，只要有其它的系統編程 語言。Java倒了就倒了唄，未必我不能用.NET?Ruby曇花一現又如何。假如用得不爽，換到其它動態語言就是了。J2EE被廢了又怎樣?未必我們就 做不出分布系統了?這里還舉了更多的例子?！ ∫痪湓?，只有人是真正的銀彈。職業發展的目標，就是把自己變成銀彈。那時候，你就不再是人，而是人彈。 最后就以我在Bjarne的眾多訪談當中摘錄的一些關于如何學習C++(以及編程)的看法結束吧(沒空逐段翻譯了，只將其中我覺得最重要的幾段譯了一下，當然，其它也很重要，這些段落是在Bjarne的所有采訪稿中摘抄出來的，所以強烈建議都過目一下)： I suspect that people think too little about what they want to build, too little about what would make it correct, and too much about "efficiency" and following fashions of programming style. The key questions are always: "what do I want to do?" and "how do I know that I have done if?". Strategies for testing enters into my concerns from well before I write the firat line of code, and that despite my view that you have to write code very early - rather than wait until a design is complete. 譯：我感覺人們過多關注了所謂“效率”以及跟隨編程風格的潮流，卻嚴重忽視了本不該被忽視的問題，如“我究竟想要構建什么樣的系統”、“怎樣才能使它正確”。最要害的問題永遠是：“我究竟想要做什么?”和“如何才能知道我的系統是否已經完成了呢?”就拿我來說吧，我會在編寫第一行代碼之前就考慮測試方案，而且這還是在我關于應當早于設計完成之前就進行編碼的觀點的前提之下?！ bviously, C++ is very complex. Obviously, people get lost. However, most peple get lost when they get diverted into becoming language lawyers rather than getting lost when they have a clear idea of what they want to eXPress and simply look at C++ language features to see how to express it. Once you know data absreaction, class hierarchies (object-oriented programming), and parameterization with types (generic programming) in a fairly general way, the C++ language features fall in place. 譯：誠然，C++非常復雜。誠然，人們迷失其中了。然而問題是，大多數人不是因為首先對自己想要表達什么有了清楚的熟悉只不過在去C++語言中搜尋合適的語言特性時迷失的，相反，大多數人是在不覺成為語言律師的路上迷失在細節的叢林中的。事實是，只需對數據抽象、類體系結構(OOP)以及參數化類型(GP)有一個相當一般層面的了解，C++紛繁的語言特性也就清楚起來了?！ ell, I don't think I made such a trade-off. I want elegant and efficient code. Sometimes I get it. These dichotomies (between efficiency versus correctness, efficiency versus programmer time, efficiency versus high-level, et cetera.) are bogus. I think the real problem is that "we" (that is, we software developers) are in a permanent state of emergency, grasping at straws to get our work done. We perform many minor miracles through trial and error, excessive use of brute force, and lots and lots of testing, but--so often--it's not enough. Software developers have become adept at the difficult art of building reasonably reliable systems out of unreliable parts. The snag is that often we do not know exactly how we did it: a system just "sort of evolved" into something minimally acceptable. Personally, I prefer to know when a system will work, and why it will. There are more useful systems developed in languages deemed awful than in languages praised for being beautiful--many more. The purpose of a programming language is to help build good systems, where "good" can be defined in many ways. My brief definition is, correct, maintainable, and adequately fast. Aesthetics matter, but first and foremost a language must be useful; it must allow real-world programmers to express real-world ideas succinctly and affordably. I'm sure that for every programmer that dislikes C++, there is one who likes it. However, a friend of mine went to a conference where the keynote speaker asked the audience to indicate by show of hands, one, how many people disliked C++, and two, how many people had written a C++ program. There were twice as many people in the first group than the second. Expressing dislike of something you don't know is usually known as prejudice. Also, complainers are always louder and more certain than proponents--reasonable people acknowledge flaws. I think I know more about the problems with C++ than just about anyone, but I also know how to avoid them and how to use C++'s strengths. In any case, I don't think it is true that the programming languages are so difficult to learn. For example, every first-year university biology textbook contains more details and deeper theory than even an expert-level programming-language book. Most applications involve standards, Operating systems, libraries, and tools that far exceed modern programming languages in complexity. What is difficult is the appreciation of the underlying techniques and their application to real-world problems. Obviously, most current languages have many parts that are unnecessarily complex, but the degree of those complexities compared to some ideal minimum is often exaggerated. We need relatively complex language to deal with absolutely complex problems. I note that English is arguably the largest and most complex language in the world (measured in number of Words and idioms), but also one of the most successful. C++ provides a nice, extended case study in the evolutionary approach. C compatibility has been far harder to maintain than I or anyone else expected. Part of the reason is that C has kept evolving, partially guided by people who insist that C++ compatibility is neither necessary nor good for C. Another reason-- probably even more important--is that organizations prefer interfaces that are in the C/C++ subset so that they can support both languages with a single effort. This leads to a constant pressure on users not to use the most powerful C++ features and to myths about why they should be used "carefully," "infrequently," or "by experts only." That, combined with backwards-looking teaching of C++, has led to many failures to reap the potential benefits of C++ as a high-level language with powerful abstraction mechanisms. The question is how deeply integrated into the application those system dependencies are. I prefer the application to be designed conceptually in isolation from the underlying system, with an explicitly defined interface to "the outer world," and then integrated through a thin layer of interface code. Had I had a chance to name the style of programming I like best, it would have been "class-oriented programming", but then I'm not particularly good at finding snappy names. The school of thought that I belong to - rooted in Simula and related design philosophies - emphasizes the role of compile-time checking and flexible (static) type systems. Reasoning about the behavior of a program has to be rooted in the (static) structure of the source code. The focus should be on guarantees, invariant, etc. which are closely tied to that static structure. This is the only way I know to effectively deal with correctness. Testing is essential but cannot be systematic and complete without a good internal program structure - simple-minded blackbox testing of any significant system is infeasible because of the exponential explosion of states. So, I recommend people to think in terms of class invariants, exception handling guarantees, highly structured resource management, etc. I should add that I intensely dislike debugging (as ah hoc and unsystematic) and strongly prefer reasoning about source code and systematic testing. Pros: flexibility, generality, performance, portability, good tool support, available on more platforms than any competitor except C, access to hardware and system resources, good availability of programmers and designers. Cons: complexity, sub-optimal use caused by poor teaching and myths.
