This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of CD1 status.

### 200. Forward iterator requirements don't allow constant iterators

Section: 25.3.5.5 [forward.iterators] Status: CD1 Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2016-01-28

Priority: Not Prioritized

View all other issues in [forward.iterators].

View all issues with CD1 status.

Discussion:

In table 74, the return type of the expression `*a` is given as `T&`, where `T` is the iterator's value type. For constant iterators, however, this is wrong. ("Value type" is never defined very precisely, but it is clear that the value type of, say, `std::list<int>::const_iterator` is supposed to be `int`, not `const int`.)

Proposed resolution:

In table 74, in the `*a` and `*r++` rows, change the return type from "`T&`" to "`T&` if `X` is mutable, otherwise `const T&`". In the `a->m` row, change the return type from "`U&`" to "`U&` if `X` is mutable, otherwise `const U&`".

[Tokyo: The LWG believes this is the tip of a larger iceberg; there are multiple const problems with the STL portion of the library and that these should be addressed as a single package. Note that issue 180 has already been declared NAD Future for that very reason.]

[Redmond: the LWG thinks this is separable from other constness issues. This issue is just cleanup; it clarifies language that was written before we had iterator_traits. Proposed resolution was modified: the original version only discussed *a. It was pointed out that we also need to worry about *r++ and a->m.]