Re: map vs. set (stl)

From:

John Harrison <john_andronicus@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 23 May 2007 20:29:28 GMT

Message-ID:

<Iu15i.1237$rW2.751@newsfe7-win.ntli.net>

Qwavel wrote:

Let's say I have something like this, where 'name' is a POD type, and
'value' is a class.

std::map< name, value >

But then I realize that 'name' should actually be one of the members
of 'value' class, so I have a redundancy. I then switch and start
using std::set< value >. To make 'value' suitable for this purpose, I
make it look like this...

class value {
  const int name;
  bool operator<( const value& rhs ) const
     { return name < rhs.name; }
  void operator=( const value& rhs );
  ...
};

This now satisfies the requirements of a set, and it works. Great.
But I feel as though I have really strayed far from the idea of a
set. For example, the key part of my value is constant, but the whole
value is not.

Should I really be using a set like this?

I think it's always worth refining your design so that it's natural, so
it feels right. You seem to be thinking about the value class solely in
terms of it's role within the set. Try thinking about the value class
independently instead of how you might be using it in a map or set.

You might find that a custom comparator for a set is the way to go.

john