如何为类方法提供STL容器以进行延迟评估？

Question

I'm trying to implement a parallel data gathering with consequent single-task data processing. Parallel task would gather data into a number of vectors then pass the collected containers into a single-task processing class. Once all the gatherers complete the data gathering, the processing stage would commence.

However, I'm confused at how to implement a processing class members that would hold the gathered data. I cannot make them references to vectors because references should be initialized at the processing object initialization time. I probably cannot make them pointers to vectors because pointer fiddling is discouareged. I also cannot make them another bunch of vectors to avoid the unnecessary data copying during the assignment operations.

How should I design the internals of the processing class to bypass those limitations?

Answer 1

The answer is in your question - "...gather data into a number of vectors then pass the collected containers..."

You can make your internal data structures std::vector and pass the outside data using move and swap them with the internal vectors:

class foo
{
    public:
        void set_vector(std::vector<int>&& vector)
        {
            std::swap(internal_vector, vector);
        }

        void alternative_set_vector(std::vector<int>& vector)
        {
            std::swap(internal_vector, vector);
        }

    private:
        std::vector<int> internal_vector;
};

void use_foo()
{
    foo some_foo;
    {
        std::vector<int> outside_vector;//fill outside_vector with your data
        some_foo.set_vector(std::move(outside_vector));
    }
    {
        std::vector<int> outside_vector;//fill outside_vector with your data
        some_foo.alternative_set_vector(outside_vector);
    }
}

The version with alternative_set_vector works fine, but it's not obvious for the calling code that the vector will be "filled" with some "random" values after the call.