Why is std::iterator deprecated?

Question

Template class std::iterator is set to be deprecated in C++17. Why so? It has been a handy way to make sure std::iterator_traits works, especially if you can make use of the default template arguments. Is there some other way of doing it in C++17?

Answer 1

As Barry states, the working group has decided that explicitly declaring the types in the class is more readable and leads to less surprises than inheriting from std::iterator.

It's not too hard, though, to convert to the explicit types (below example taken from www.fluentcpp.com here). Given a class that was declared like so:

class MyIterator
  : public std::iterator<std::forward_iterator_tag, int, int, int*, int&>
{
  ...

The class without std::iterator becomes:

class MyIterator
{
public:
    using iterator_category = std::forward_iterator_tag;
    using value_type = int;
    using difference_type = int;
    using pointer = int*;
    using reference = int&;

    // ...