[ 學習筆記 ] Effective C++ ：Item 1

Item 1：View C++ as a federation of languages

 Item 1：将C++視為語言的聯合體

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 最初，C++僅僅是在C的基礎上附加了一些面向對象的特征。但是，随着C++的成長發展，C++已經成為了一個多範式的程式設計語言，一個囊括了過程化，面向對象，函數化，泛型以及元程式設計特性的聯合體。可以将它分成4個部分：

 C ------ 歸根結底，C++依然是基于C的。子產品，語句，預處理器，内建資料類型，數組，指針等，全都來自于C。隻是在很多方面，C++提出了更進階的解決問題的方法。

 Object-Oriented C++ ------ C++的這部分就是C with Classes 涉及到的全部：類（包括構造函數和析構函數），封裝，繼承，多态，虛函數（動态邦定）等。C++的這一部分直接适用于面向對象設計的經典規則。

 Template C++ ------ 這是C++的泛型程式設計部分。

 STL ------ STL是一個特殊的模闆庫。它将容器，疊代器，算法和函數對象優雅的整合在一起。

頭腦中保持這四個子語言，從一種子語言轉到另一種時，為了高效程式設計，需要改變政策：

 例如，适用内建（類C的）類型時，傳值通常比傳引用更高效，但是當從C++的C部分轉到C++的Object-Oriented部分，使用者自定義構造函數和析構函數意味着更好的做法是将引用傳遞給const參數。在 Template C++ 中工作時，這一點更加重要，因為，在這種情況下，你甚至不知道你的操作涉及到的對象的類型。當你進入 STL，無論如何，你知道疊代器和函數對象以 C 的指針為原型，對于 STL 中的疊代器和函數對象，古老的 C 中的傳值規則又重新生效。

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 Things to Remember：

 高效C++程式設計規則的變化，依賴于你使用C++的哪一個部分。

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 In the beginning, C++ was just C with some object-oriented features tacked on. As the language matured, C++ have become a multiparadigm programming language, one suppoting a combination of procedural, object-oriented, functional, generic, and metaprogramming features.

 There are four parts in the C++:

 C ------ Way down deep, C++ is still based on C. Blocks, statements, the preprocessor, built-in data types, arrays, pointers,etc, all come from C. In many cases, C++ just offers approaches to problems that are superior to their C counterparts.

 Object-Oriented C++ ------ This part of C++ is what C with Classes was all about: classes(including constructors and destructors), encapsulation, inheritance, polymorphism, virtual functions(dynamic binding),etc. This is the part of C++ to which the classic rules for object-oriented design most directly apply.

 Template C++ ------ This is the generic programming part of C++.

 The STL ------ The STL si avery special template library. Its conventions regarding containers, iterators, algorithms, and function objects mesh beautifully.

 Keep these four sublanguages in mind, and don't be surprised when you encounter situations where effective programming requires that you change strategy when you switch from one sublanguage to another.

 For example, pass-by-value is generally more efficient than pass-by-reference for built-in (i.e., C-like) types, but when you move from the C part of C++ to Object-Oriented C++, the existence of user-defined constructors and destructors means that pass-by-reference-to-const is usually better. This is especially the case when working in Template C++, because there, you don't even know the type of object you're dealing with. When you cross into the STL, however, you know that iterators and function objects are modeled on pointers in C, so for iterators and function objects in the STL, the old C pass-by-value rule applies again.  

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 Things to Remember

 Rules for effective C++ programming vary, depending on the part of C++ you are using!