Question

Good Day,

Assume that I am writing a Python-like range in C++. It provides all the characteristics of Random Access containers(Immutable of course). A question is raised in my mind about the following situation:

I have two different iterators, that point to different instances of the range container. The thing is that these two ranges are equal. i.e. they represent the same range. Would you allow the following situation:

fact: range1 == range2 e.g.
---------------------------
range range1(10, 20, 1), range2((10, 20, 1);
range::iterator i = range1.begin(), j = range2.begin();
assert(i == j); // would you allow this?

Sorry if I am missing a simple design rule in STL 🙂

Answer 1

By default, in the STL, two iterators from two different container are not comparable. This means, the behavior is unspecified. So you do whatever you want, nobody should even try.

edit

After looking carefully at the standard, section 24.1, paragraph 6 states:

An iterator j is called reachable from
an iterator i if and only if there is
a finite sequence of applications of
the expression ++i that makes i == j.
If j is reachable from i, they refer
to the same container.

Which means that if you allow i == j with i and j in two different container, you really consider both container as being the same. As they are immutable, this is perfectly fine. Just a question of semantic.