6
\$\begingroup\$

I have this very simple template:

#include <algorithm>
#include <initializer_list>
#include <iostream>
#include <iterator>
#include <list>
#include <set>
#include <vector>

template<class Container>
class ImmutableContainerView {
private:
    Container& my_container;
public:
    ImmutableContainerView(Container& container) :
    my_container {container} {}

    typename Container::const_iterator cbegin() const {
        return my_container.cbegin();
    }

    typename Container::const_iterator cend() const {
        return my_container.cend();
    }

    typename Container::const_reverse_iterator crbegin() const {
        return my_container.crbegin();
    }

    typename Container::const_reverse_iterator crend() const {
        return my_container.crend();
    }

    typename Container::size_type size() const {
        return my_container.size();
    }

    bool empty() const {
        return my_container.empty();
    }
};

int main(int argc, const char * argv[]) {
    std::initializer_list<int> il = { 1, 2, 4, 5, 6 };

    std::list<int>   my_list   = il;
    std::set<int>    my_set    = il;
    std::vector<int> my_vector = il;

    ImmutableContainerView<std::list<int>>   my_immutable_list(my_list);
    ImmutableContainerView<std::set<int>>    my_immutable_set(my_set);
    ImmutableContainerView<std::vector<int>> my_immutable_vector(my_vector);

    // Iterators:
    std::ostream_iterator<int> out_it (std::cout, ", ");
    std::copy(my_immutable_list.cbegin(), my_immutable_list.cend(), out_it);
    std::cout << "\n";

    std::copy(my_immutable_set.cbegin(), my_immutable_set.cend(), out_it);
    std::cout << "\n";

    std::copy(my_immutable_vector.cbegin(), my_immutable_vector.cend(), out_it);
    std::cout << "\n";

    // Reversed iterators:
    std::copy(my_immutable_list.crbegin(), my_immutable_list.crend(), out_it);
    std::cout << "\n";

    std::copy(my_immutable_set.crbegin(), my_immutable_set.crend(), out_it);
    std::cout << "\n";

    std::copy(my_immutable_vector.crbegin(), my_immutable_vector.crend(), out_it);
    std::cout << "\n";

    // Size:
    std::cout << my_immutable_list.size() << "\n";
    std::cout << my_immutable_set.size() << "\n";
    std::cout << my_immutable_vector.size() << "\n";

    // Empty:
    std::cout << std::boolalpha;
    std::cout << my_immutable_list.empty() << "\n";
    std::cout << my_immutable_set.empty() << "\n";
    std::cout << my_immutable_vector.empty() << "\n";

    return 0;
}

I would like to hear comments on how to improve it. In particular, is it possible to do some metaprogramming trickery such that it can adapt to different containers; for example, it could provide operator[size_t] for std::vector, but find for std::set?

\$\endgroup\$
8
\$\begingroup\$

Your view isn't immutable, though immutability might be a property of the underlying object. It's a constant view, meaning the underlying object might change, but not from that view. The canonical way to get a constant view is by the way to use a constant reference, unless the view should erase some of the differences between underlying containers, like std::string_view does.


You are missing .begin(), .end(), .rbegin() and .rend().

Your view is constant, fine, but forcing everyone to explicitly say so for each function-call breaks interface conventions.

The missing functions are the common interface, the ones you provided just optional convenience-functions for calling manually which might not be provided even if possible, and certainly never used in generic code. Take a look at <iterator> and the free functions for accessing any generic range there.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.