我的意思是,除了它的名字标准模板库(后来演变成c++标准库)。

c++最初将面向对象的概念引入到C中,也就是说:您可以根据特定实体的类和类层次结构来判断它能做什么和不能做什么(不管它是如何做的)。由于多重继承的复杂性,一些能力的组合更难以用这种方式描述,而且c++以一种有点笨拙的方式支持仅接口继承(与java等相比),但它确实存在(并且可以改进)。

然后模板开始发挥作用,还有STL。STL似乎采用了经典的OOP概念,并将它们冲入下水道,取而代之的是使用模板。

当模板用于泛化类型时,类型本身与模板的操作无关(例如容器),这两种情况之间应该有区别。vector<int>非常有意义。

然而,在许多其他情况下(迭代器和算法),模板化类型应该遵循一个“概念”(Input Iterator, Forward Iterator,等等),其中概念的实际细节完全由模板函数/类的实现定义,而不是由模板使用的类型的类定义,这在某种程度上是对OOP的反使用。

例如,你可以告诉函数:

void MyFunc(ForwardIterator<...> *I);

更新:由于在最初的问题中不清楚,ForwardIterator本身可以被模板化以允许任何ForwardIterator类型。相反,将ForwardIterator作为一个概念。

只有通过查看它的定义才能期望Forward Iterator,在这里你需要查看以下方面的实现或文档:

template <typename Type> void MyFunc(Type *I);

我可以提出两个主张来支持使用模板:通过为每个使用的类型重新编译模板,而不是使用动态分派(主要通过虚表),可以使编译后的代码更加高效。2. 事实上,模板可以与原生类型一起使用。

然而,我正在寻找一个更深刻的原因,放弃经典的面向对象的支持模板的STL?


当前回答

最基本的问题是

void MyFunc(ForwardIterator *I);

你如何安全地获取迭代器返回的东西的类型?对于模板,这是在编译时为您完成的。

其他回答

“面向对象编程对我来说只意味着消息传递、状态过程的本地保留、保护和隐藏,以及所有事情的极端后期绑定。它可以在Smalltalk和LISP中完成。可能还有其他系统也有这种可能,但我不知道它们。”——Alan Kay (Smalltalk的创造者)

c++、Java和大多数其他语言都与经典的OOP相去甚远。也就是说,为意识形态争论并不是特别有效。c++在任何意义上都不是纯粹的,所以它实现的功能在当时似乎是有实用意义的。

对于我认为你在问或抱怨的问题,最直接的回答是:假设c++是一种面向对象语言是一个错误的假设。

c++是一种多范式语言。它可以使用面向对象原则编程,可以程序化编程,也可以泛型编程(模板),使用c++ 11(以前称为c++ 0x)甚至可以对某些东西进行函数式编程。

c++的设计者认为这是一种优势,所以他们会争辩说,当泛型编程能更好地解决问题,并且更通用地解决问题时,限制c++像纯粹的面向对象语言一样运行将是一种倒退。

STL最初的目的是提供一个涵盖最常用算法的大型库,其目标是一致的行为和性能。模板是使实现和目标可行的关键因素。

只是为了提供另一个参考:

1995年3月,《DDJ》的艾尔·史蒂文斯采访亚历克斯·斯捷潘诺夫:

http://www.sgi.com/tech/stl/drdobbs-interview.html

Stepanov解释了他的工作经验和对大型算法库的选择,最终演变为STL。

Tell us something about your long-term interest in generic programming .....Then I was offered a job at Bell Laboratories working in the C++ group on C++ libraries. They asked me whether I could do it in C++. Of course, I didn't know C++ and, of course, I said I could. But I couldn't do it in C++, because in 1987 C++ didn't have templates, which are essential for enabling this style of programming. Inheritance was the only mechanism to obtain genericity and it was not sufficient. Even now C++ inheritance is not of much use for generic programming. Let's discuss why. Many people have attempted to use inheritance to implement data structures and container classes. As we know now, there were few if any successful attempts. C++ inheritance, and the programming style associated with it are dramatically limited. It is impossible to implement a design which includes as trivial a thing as equality using it. If you start with a base class X at the root of your hierarchy and define a virtual equality operator on this class which takes an argument of the type X, then derive class Y from class X. What is the interface of the equality? It has equality which compares Y with X. Using animals as an example (OO people love animals), define mammal and derive giraffe from mammal. Then define a member function mate, where animal mates with animal and returns an animal. Then you derive giraffe from animal and, of course, it has a function mate where giraffe mates with animal and returns an animal. It's definitely not what you want. While mating may not be very important for C++ programmers, equality is. I do not know a single algorithm where equality of some kind is not used.

最基本的问题是

void MyFunc(ForwardIterator *I);

你如何安全地获取迭代器返回的东西的类型?对于模板,这是在编译时为您完成的。

The concept of separating interface from interface and being able to swap out the implementations is not intrinsic to Object-Oriented Programming. I believe it's an idea that was hatched in Component-Based Development like Microsoft COM. (See my answer on What is Component-Driven Development?) Growing up and learning C++, people were hyped out inheritance and polymorphism. It wasn't until 90s people started to say "Program to an 'interface', not an 'implementation'" and "Favor 'object composition' over 'class inheritance'." (both of which quoted from GoF by the way).

然后,Java出现了内置的垃圾收集器和接口关键字,突然之间,将接口和实现分开变得可行了。不知不觉,这个想法就成为了OO的一部分。c++、模板和STL的出现要早于这一切。