Why does C++ not provide a First-In-First-Out singly-linked list?

Question

In the C++ standard library, list is doubly-linked list; forward_list is singly-linked list but supports Last-In-First-Out only.

However, the First-In-First-Out singly-linked list has been widely used for its low space-overhead than other list-like containers (except forward_list). So I wonder:

Why does C++ not provide a First-In-First-Out singly-linked list?

Answer 1

You can easily create one yourself by augmenting forward_list with a before-the-end iterator to implement back() and push_back():

template<class T>
struct fifo_list {
    std::forward_list<T> base;
    std::forward_list<T>::iterator before_end = base.before_begin();
    fifo_list(fifo_list const& other) { for (auto t : other.base) push_back(t); }
    fifo_list(fifo_list&&) = default;
    auto front() { return base.front(); }
    void pop_front() { base.pop_front(); }
    auto back() { return *before_end; }
    void push_back(T t) { before_end = base.insert_after(before_end, t); }
};

This can then be used with the std::queue adapter.

The overhead associated with maintaining the before_end iterator is presumably the reason why this facility (back and push_back) is not included in forward_list already.