Zachary Turner wrote:
Has this been considered before, and can anyone think of any technical limitations that would prevent such a class to be written?
Lazy lists typically rely on a garbage collector to clean up nodes that aren't used anymore. You can achieve the same effect with reference-counting pointers to each node, but the overhead would be significant. The second problem with the implementation is state. It's rather tricky to correctly keep state in such a list, especially if you want to allow discarding and re-evaluating older list nodes. This requires that the function in question returns a tuple (next value, next function), which makes the overhead grow further and is really unidiomatic to program in C++. Also, lazy lists are really an idiom from languages that are very comfortable with lists, i.e. mostly functional languages (Haskell, for example). The same idiom is, I believe, really not as practical in C++ and other imperative languages. Modern C++ uses iterator ranges as the primary concept for generic handling of finite and infinite sequences, and there already are function-backed input iterators. The second concept used is input streams. Do you have a motivating use case for such lists? Sebastian