返回类型为“ input_iterator :: operator *”？

Question

I'm doing an input iterator wrapper for a QSqlQuery (for traversing rows and constructing a new class type object for each row), and I want to know what must be the returned type of operator* .

According to cppreference in the input iterator concept description , the returned type of *i must be:

reference, convertible to value_type

and curiously, I'm in doubt about if that comma , represent an or or and and ("reference to value_type or/and convertible to value_type"), because in my case, I construct a new object (whose type is a class template parameter) when calling operator* . Consequently, I cannot return a reference.

To match the input iterator "concept", can I return the object by value?

Answer 1

iterator_traits<> must define 5 types, one of which is reference , hence the comma. You can return by value; it's only fair to do so for const_iterator , thought: for non-const, you cannot modify the original. I guess this is ok here as you have an sql query. In this case you do typedef value_type reference; inside iterator_traits<T> .