如何正确实现自定义迭代器和 const_iterators?

How to correctly implement custom iterators and const_iterators?(如何正确实现自定义迭代器和 const_iterators?)

问题描述

我有一个自定义容器类，我想为其编写 iterator 和 const_iterator 类.

I have a custom container class for which I'd like to write the iterator and const_iterator classes.

我以前从未这样做过，也没有找到合适的方法.关于迭代器创建的准则是什么?我应该注意什么?

I never did this before and I failed to find an appropriate how-to. What are the guidelines regarding iterator creation, and what should I be aware of ?

我还想避免代码重复(我觉得 const_iterator 和 iterator 共享很多东西；一个应该继承另一个吗?).

I'd also like to avoid code duplication (I feel that const_iterator and iterator share many things; should one subclass the other ?).

脚注:我很确定 Boost 可以缓解这种情况，但由于许多愚蠢的原因，我不能在这里使用它.

推荐答案

• 选择适合您容器的迭代器类型:输入、输出、转发等.
• 使用标准库中的基迭代器类.例如，std::iterator 和 random_access_iterator_tag.这些基类定义了 STL 所需的所有类型定义并完成其他工作.

• 为避免代码重复，迭代器类应该是一个模板类，并通过值类型"、指针类型"、引用类型"或全部参数化(取决于实现).例如:

  • Choose type of iterator which fits your container: input, output, forward etc.
  • Use base iterator classes from standard library. For example, std::iterator with random_access_iterator_tag.These base classes define all type definitions required by STL and do other work.

  • To avoid code duplication iterator class should be a template class and be parametrized by "value type", "pointer type", "reference type" or all of them (depends on implementation). For example:

    // iterator class is parametrized by pointer type
    template <typename PointerType> class MyIterator {
        // iterator class definition goes here
    };
    
    typedef MyIterator<int*> iterator_type;
    typedef MyIterator<const int*> const_iterator_type;
    

    注意 iterator_type 和 const_iterator_type 类型定义:它们是非常量和 const 迭代器的类型.

    Notice iterator_type and const_iterator_type type definitions: they are types for your non-const and const iterators.

    另请参阅:标准库参考

    std::iterator 自 C++17 起已弃用.查看相关讨论此处.

    std::iterator is deprecated since C++17. See a relating discussion here.

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