[boost] preferred idiom for "occasional properties"

From: joel reed (joel.reed_at_[hidden])
Date: 2005-11-01 13:13:48

I've been exploring what a cross platform process library would look like
and have a question about whether there is a preferred idiom for what I'll
call an occasional property for lack of a better term.

Given a process, I'd like to be able to query the parent process. Posix has
such a notion, but win32 doesn't. On posix, afaik, every process has a
parent except for "init."

I can't decide whether I should say

class process
{
  public:
    process parent();

    static const process nprocess; // like std::string's npos
};

where parent() != nprocess when the process has a parent.

or 

class process
{
  public:
     typedef std::pair<process,bool> parent_type;
     parent_type parent();
};

where parent_type.second == true when the process has a parent.

I also considered a "parent_iterator", since on posix, you could keep
walking backwards up the hierarchy till you get to init, e.g.

class parent_iterator;

class process
{
  public:
    parent_iterator parent();
};

but conceptually, I couldn't see a good "end()"

Anyone care to offer an idea for the best way to handle this?

jr