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?
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.