Re: hasMember

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 10 Dec 2010 02:01:19 -0800 (PST)

Message-ID:

<51bad171-300f-4489-a2ae-3e900197196e@y23g2000yqd.googlegroups.com>

On Dec 9, 1:16 pm, Jeff Flinn <TriumphSprint2...@hotmail.com> wrote:

James Kanze wrote:

On Dec 9, 7:01 am, Paavo Helde <myfirstn...@osa.pri.ee> wrote:

Andrea Crotti <andrea.crott...@gmail.com> wrote innews:m11v5rrcno.fsf@ip1-201.halifax.rwth-aachen.de:

Jeff Flinn <TriumphSprint2...@hotmail.com> writes:

To avoid the memory allocation and ownership issues use
boost::optional.

  #include <boost/optional.hpp>

  typedef boost::optional<int> optional_int;

  optional_int Cont::getValue(int idx) const
  {
     std::map<int, int>::const_iterator itr = content.find(idx);
     return (itr != cont.end())? itr->second : optional_int();
  }

and:

  if(optional_int i = obj.getValue(idx)) // safe bool idiom
  {
     int x = *i + 123; // deref for value
  }

Using exceptions in this case could be good?

Seems out of place for the use you've described, given what little
info you've provided.

Interesting the optional_int, but I can't use boost...

I'm sure boost::optional is quite easy (and instructive) to implement by
yourself.

Except that he really needs optional<int&>. Which in turn means

Where did this requirement come from?

The fact that he's implemention a (map-like) container.

--
James Kanze