应该如何实现大小受限的 stl 类容器? [英] How should a size-limited stl-like container be implemented?

问题描述

在重构时，我想更改将条目添加到 std::vector 的数组，但为了兼容性(持久性、降级等)，它仍然需要有一个上限.
拥有一个大小有限的 stl 类容器的最佳方法是什么(优雅的、类似 stl 的、有限的额外代码)，因此您知道插入条目会失败?

While refactoring, I wanted to change an array where entries are added to an std::vector, but for compatibility (persistency, downgrading,...), it still needs to have an upper limit.
What is the best way (elegant, stl-like, limited extra code) to have an stl-like container which is limited in size, so you know that inserting an entry fails?

编辑:
澄清一下:我想要一个类似 stl 的容器，它开始是空的，您可以填充条目并可能删除条目并迭代填充的条目，但这不允许放入超过例如50 个条目，几乎就像一个连续的限制器，但有一个上限.

Edit:
To clarify: I would like an stl-like container, that starts empty, that you can fill with entries and possibly remove entries and that iterate over the filled-in entries, but that doesn't allow to put in more than e.g. 50 entries, so almost like a sequential contrainer, but with an upper-limit.

推荐答案

一个简单的解决方案是在您自己的有限大小的容器中封装一个向量.您可以使用私有组合或私有继承——注意私有继承模型实现并且没有公共继承的一些缺点.

A simple solution would be encapsulating a vector inside your own limited size container. You could use private composition or private inheritance --note that private inheritance models implemented in terms of and does not have some of the shortcomings of public inheritance.

编辑:具有私有继承的解决方案草图

EDIT: Sketch of the solution with private inheritance

template <typename T, unsigned int N>
class fixed_vector : std::vector<T>
{
    typedef std::vector<T> vector_type;
public:
    typedef typename vector_type::reference reference;
    typedef typename vector_type::const_reference const_reference;
    typedef typename vector_type::iterator iterator;
    typedef typename vector_type::const_iterator const_iterator;
    typedef typename vector_type::value_type value_type;
    typedef typename vector_type::size_type size_type;

    fixed_vector() : vector_type() {}
    fixed_vector( size_type size, value_type const & value = value_type() )
       : vector_type(size,value)
    {}      

    void push_back( value_type v ) {
        ensure_can_grow();
        vector_type::push_back( v );
    }
    iterator insert( iterator position, value_type const & v ) {
        ensure_can_grow();
        vector_type::insert( position, v );
    }
    void reserve( size_type size ) {
        if ( size > N ) throw std::invalid_argument();
        vector_type::reserve( size );
    }
    size_type capacity() const {
        // In case the default implementation acquires by default 
        // more than N elements, or the vector grows to a higher capacity
        return std::min( vector_type::capacity(), N );
    }
    // provide other insert methods if required, with the same pattern
    using vector_type::begin;
    using vector_type::end;
    using vector_type::operator[];
    using vector_type::erase;
    using vector_type::size;
    using vector_type::empty;
private:
    void ensure_can_grow() const {
        // probably a different exception would make sense here: 
        if ( this->size() == N ) throw std::bad_alloc();
    }
};

那里有相当多的挥手... std::vector 接受更多可以添加到外观的参数.如果您需要任何其他方法或 typedef，您可以使用 using 声明将它们引入范围，重新定义 typedef，或使用您的特定测试实现适配器.

There is quite a bit of hand-waving there... std::vector take more arguments that could be added to the façade. If you need any of the other methods or typedefs, you can just bring them into scope with a using declaration, redefine the typedef, or implement the adaptor with your particular test.

此外，在这个实现中，大小是一个编译时常量，但将其修改为构造函数参数会非常简单.

Also, in this implementation the size is a compile time constant, but it would be really simple to modify it into a constructor parameter.

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