Question

Both SGI slist and C++11 std::forward_list appear identical to me unless I have missed something; both implement a singly-linked list.

I assume there is a difference though as the C++ Standard Commitee didn’t adopt the name slist and instead chose a new name, forward_list, when they added the container into the Standard Library for C++0x.

Answer 1

One major difference is that std::forward_list lacks a size() member function, where as the sgi::slist doesn’t. The motivation for this is that an O(N) size() has been problematic. N2543 has more details on the design decisions for forward_list.

Update:

I recently had a good excuse to look closer at this subject. slist also has other member functions that one would be tempted to think are O(1), but are really O(N). These include:

iterator previous(iterator pos);
const_iterator previous(const_iterator pos) const;
iterator insert(iterator pos, const value_type& x);
iterator erase(iterator pos);
void splice(iterator position, slist& x);
void splice(iterator position, slist& x, iterator i);

In short, if you’re not very careful, you can end up with significant performance problems by using slist. Use of std::forward_list instead ensures that you’ll get the expected O(1) performance out of your singly linked list.