[odb-users] odb::result<T> does not contain members "const_iterator" and "end () const".

[Jeroen N. Witmond [Bahco]]

Hi Boris,

Boris Kolpackov wrote:
> Hi Jeroen,
>
> Jeroen N. Witmond [Bahco] <jnw at xs4all.nl> writes:
>
>> While experimenting with ODB I noticed that odb::result<T> does not
>> contain members "const_iterator" and "end () const".
>
> Result is a stream-like object and result::iterator is an input
> iterator. In this light, it doesn't make much sense to have a
> const_iterator since advancing the iterator changes the result.
>
>
>> The compiler noticed it, anyway. :-)
>
> Can you show the code fragment that triggered it?

#include <iostream>
#include <odb/database.hxx>

/* This class should be in a separate .hpp file and contain some
 * #pragmas. The generated odb.hxx file should be included. However,
 * the current content is sufficient to demonstrate the use of const.
 */
class FourPoint
{
public:
  double latitude;
};

typedef odb::result<FourPoint> result;

inline std::ostream& operator<<(std::ostream& out, const result& val)
{
  for (result::const_iterator i (val.begin ()); i != val.end (); ++i)
    out << *i << std::endl;
  return out;
}

This code results in the following errors:

noconstiter.cpp: In function ‘std::ostream& operator<<(std::ostream&,
const result&)’:
noconstiter.cpp:18:8: error: ‘const_iterator’ is not a member of ‘result
{aka odb::result<FourPoint>}’
noconstiter.cpp:18:31: error: expected ‘;’ before ‘i’
noconstiter.cpp:18:49: error: ‘i’ was not declared in this scope
noconstiter.cpp:18:63: error: no matching function for call to
‘odb::result<FourPoint>::end() const’
noconstiter.cpp:18:63: note: candidate is:
In file included from /usr/local/include/odb/prepared-query.hxx:12:0,
                 from /usr/local/include/odb/database.hxx:27,
                 from noconstiter.cpp:2:
/usr/local/include/odb/result.hxx:176:5: note: odb::result<T>::iterator
odb::result<T>::end() [with T = FourPoint; odb::result<T>::iterator =
odb::result_iterator<FourPoint, (odb::class_kind)2u>] <near match>
/usr/local/include/odb/result.hxx:176:5: note:   no known conversion for
implicit ‘this’ parameter from ‘const result* {aka const
odb::result<FourPoint>*}’ to ‘odb::result<FourPoint>*’

Removing all consts in this operator<< results in working code.

Regards,

Jeroen.