Boost C++ Libraries: Ticket #5930: data() for iterator_range

Steven Watanabe — Fri, 23 Sep 2011 17:35:22 GMT

What exactly is iterator_range::data supposed to return?

Fri, 23 Sep 2011 19:43:35 GMT

return empty() ? NULL : &front();

Steven Watanabe — Fri, 23 Sep 2011 20:50:19 GMT

This is rather dangerous. It only works if the iterator points to contiguous storage.

Sun, 25 Sep 2011 16:59:51 GMT

Right, it should only be provided in that case.

rhys.ulerich@… — Mon, 07 Nov 2011 15:39:25 GMT

How can a member method be provided only under certain runtime conditions? It seems the existing class methods do what one needs and that data() could be written as a free function.

Mon, 07 Nov 2011 15:43:32 GMT

Replying to rhys.ulerich@…:

How can a member method be provided only under certain runtime conditions?

It's not a runtime condition.

It seems the existing class methods do what one needs and that data() could be written as a free function.

A free function that'd work for all containers / ranges that support random access would be fine too.

Mon, 07 Nov 2011 15:44:55 GMT

Except that C++11 has data() for array, string, vector and probably others, so there's probably a good reason against a free function.

rhys.ulerich@… — Mon, 07 Nov 2011 15:48:33 GMT

Referring to...

return empty() ? NULL : &front();

This is rather dangerous. It only works if the iterator points to contiguous storage.

Right, it should only be provided in that case.

I asked...

How can a member method be provided only under certain runtime conditions?

It's not a runtime condition.

An iterator_range knowing that it represents a contiguous region of memory seems like a runtime condition to me. What am I missing?

Mon, 07 Nov 2011 15:50:43 GMT

Replying to rhys.ulerich@…:

An iterator_range knowing that it represents a contiguous region of memory seems like a runtime condition to me. What am I missing?

It's a compile time condition. True for pointers, arrays, array, vector and string. False for a lot of other things.

rhys.ulerich@… — Mon, 07 Nov 2011 15:53:59 GMT

An iterator_range knowing that it represents a contiguous region of memory seems like a runtime condition to me. What am I missing?

It's a compile time condition. True for pointers, arrays, array, vector and string. False for a lot of other things.

Ahh.. Good point. My mistake.

viboes — Tue, 10 Sep 2013 20:31:37 GMT

Replying to Olaf van der Spek <olafvdspek@…>:

Right, it should only be provided in that case.

How the user could know that the function is provided only under some special circumstances? Could you show a real use case?

anonymous — Tue, 10 Sep 2013 22:41:18 GMT

I'm sure Google can give you enough real use cases for data(). It's a standard function.

status changed; resolution set

Neil Groves — Fri, 21 Feb 2014 20:23:18 GMT

status new → closed
resolution → wontfix

While a member data() function exists for some containers in the standard library it does not make sense to conditionally add this to iterator_range.

If you know enough about the iterator that this function can work then it is trivial to implement a non-member function that is more broadly applicable.

anonymous — Sat, 22 Feb 2014 10:35:59 GMT

But ISO C++ has data() as a member function, not as a non-member function.