如何使不同对象“生成器"的层次结构成为可能.在纯C ++ 11中 [英] How to make a hierarchy of different object "generators" in plain C++11

问题描述

我需要的是下面的类层次结构(在此处以草图形式提供):

What I need is the following hierarchy of classes (given here as a sketch):

class DataClass {}

class AbstractGenerator {
public:
    // Generates DataClass objects one by one. In a lazy manner
    virtual DataClass produce() = 0;
}

class RandGenerator : AbstractGenerator {
public:
    RandGenerator(int maximal_int) : maximal(maximal_int) {}
    DataClass produce() {
        // get a random number from 0 to this->maximal
        // make a DataClass object from the random int and return it
    }

private:
    int maximal;
}

class FromFileGenerator : AbstractGenerator {
public:
    FromFileGenerator(string file_name) : f_name(file_name) {}
    DataClass produce() {
        // read the next line from the file
        // deserialize the DataClass object from the line and return it
    }

private:
    string f_name;
}

我想同时支持 RandGenerator 和 FromFileGnerator 的是:

RandGenerator rg();
for (DataClass data : rg) {...}

还有一些获取生成器的前n个元素"的方法.

And also some method of taking "first n elements of the generator".

在普通的C ++ 11中，可以使用哪些合适的工具来实现此目的，或者在C ++ 11中最接近的工具是什么?

What are the appropriate tools in the plain C++11 that one could use to achieve this, or whatever is the closest to this in C++11?

推荐答案

boost::function_input_iterator is the normal tool for this job, but since you want "plain" C++, we can just reimplement the same concept.

class generator_iterator {
   std::shared_ptr<AbstractGenerator> generator;
public:
   using iterator_category = std::input_iterator_tag;
   generator_iterator(std::shared_ptr<AbstractGenerator> generator_)
       :generator(generator_) {}
   
   DataClass operator*(){return generator->produce();}
   generator_iterator& operator++(){return *this;}
   generator_iterator operator++(int){return *this;}
   //plus all the other normal bits for an output_iterator
};

然后在您的 AbstractGenerator 类中，提供 begin 和 end 方法.

And then in your AbstractGenerator class, provide begin and end methods.

generator_iterator begin() {return {this};}
generator_iterator end() {return {nullptr};} //or other logic depending on how you want to detect the end of a series

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