🚀 go-pugleaf

In article <477o7e$5pd@info.uci.kun.nl> Marian Hellema <marian@atcmp.nl> writes:

> The ObjectSpace documentation states:
> "All the items that are stored in associative containers must be
> comparable using == and <"> 
> I have not been able to find a confirmation for this rule in the
> standard working paper. Can someone clear this up for me?


All of the associative containers in the STL require that a comparison
function be defined for items in the container, but it does not
necessarily have to use operator <.  (See section 23.3 of the draft
standard.)  One of the template parameters of the associative
containers is a comparison function object used to compare items in
the container.  By default the comparison object is less<Key>, meaning
that it uses operator <, but you may provide a different type if you
want to store objects for which operator < is undefined.

(Note, incidentally, that you may pass a comparison object in the
container's constructor: each container may have its own comparison
object.  This argument defaults to Compare(), which, again, defaults
to less<Key>().)

It's still true that you must define an ordering for whatever type
you're putting in the container; you simply aren't required to use
operator <.  Associative containers that you can use for unordered
keys would also be useful, but a proposal to add them to the standard
was rejected.  

-- 
  Matt Austern                             He showed his lower teeth.  "We 
  matt@physics.berkeley.edu                all have flaws," he said, "and 
  http://dogbert.lbl.gov/~matt             mine is being wicked."

---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]

In article <477o7e$5pd@info.uci.kun.nl>,
Marian Hellema  <marian@atcmp.nl> wrote:
>
>I am using ObjectSpace's STL<Toolkit>. 
>The ObjectSpace documentation states:
>"All the items that are stored in associative containers must be
>comparable using == and <"
>
>I have not been able to find a confirmation for this rule in the
>standard working paper. Can someone clear this up for me?

My reading of 23.1.3 of the April WP indicated that operator == should
not be required by the associative containers. I havent' checked the
September WP, but I don't expect this non-requirement to have changed.

When I submitted a bug report to ObjectSpace against version 1.1.0 of
the library, I was told that they simply hadn't caught up with the
WP yet. The document accompanying version 1.2 of the library
also specifies the same requirement. Looks like they still haven't
caught up with the WP. One of the few annoying inconsistencies in an
otherwise very good implementation of STL.

-- 
Ajay Kamdar        |    Email: ajay@lehman.com    |    Standard Disclaimer 
Lehman Brothers    |    Phone: (201) 524-5048     |

[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]

In article <47ai5s$54b@jabba.lehman.com>, Ajay Kamdar <ajay@lehman.com> wrote:
>My reading of 23.1.3 of the April WP indicated that operator == should
>not be required by the associative containers. 

Typo: That should have been 23.1.2.3.

-- 
Ajay Kamdar        |    Email: ajay@lehman.com    |    Standard Disclaimer 
Lehman Brothers    |    Phone: (201) 524-5048     |

---
[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]