Re: [boost] preferred idiom for "occasional properties"

From: Joe Gottman (jgottman_at_[hidden])
Date: 2005-11-01 20:18:34

"joel reed" <joel.reed_at_[hidden]> wrote in message 
news:20051101181348.GA10833_at_ddiworld.com...
> 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()"

Why not just use boost::optional?  Then you could declare
    boost::optional<process &> parent();

One of the main uses of optional is to return data that might or might not 
exist.

Joe Gottman