Can an input iterator be dereferenced only on the right-hand sign of an assignment?

Question

I have this simple question: in C++ primer 5ed by Lippman chapter 10. "The iterator categories" it is said:

The Iterator Categories

Input iterators: can read elements in a sequence. An input iterator must provide

• Equality and inequality operators (==, !=) to compare two iterators

• Prefix and postfix increment (++) to advance the iterator

• Dereference operator (*) to read an element; dereference may appear only on the right-hand side of an assignment

• The arrow operator (->) as a synonym for (*it).member—that is, dereference the iterator and fetch a member from the underlying object.

Did he mean with "Dereference operator (*) to read an element; dereference may appear only on the right-hand side of an assignment" : on the "left side of an assignment".??

I am confused about it. Thank you.

Answer 1

The author meant that if you have an input iterator it, then you can do:

foo = *it;

but it's possible you may not be able to do:

*it = foo;

I.e. you can read from an iterator (it's on the right side of an assignment), but there is no guarantee you can write to it (it's on the left).