Re: Why are Set & Get important?

From:

"Bo Persson" <bop@gmb.dk>

Newsgroups:

comp.lang.c++

Date:

Mon, 29 Jun 2009 21:47:25 +0200

Message-ID:

<7ask20F20pnv5U1@mid.individual.net>

Jorgen Grahn wrote:

On Sun, 28 Jun 2009 13:29:53 -0700 (PDT), Daniel T.
<daniel_t@earthlink.net> wrote:

On Jun 26, 4:10 am, Bart van Ingen Schenau <b...@ingen.ddns.info>
wrote:

... exposing data members (either directly or through
getters/setters) is certainly NOT a best practice.

A member-function that returns state information about an object is
*not* exposing data members. A member-function that changes the
state of an object in some defined way is also not exposing data
members.

As a simple example:

class Range {
// private stuff
public:
// invariant: low() < high()
// invariant: high() - low() == distance()
int high() const;
int low() const;
int distance() const;
void setLow(int v);
void setDistance(int v);
};

No data member's are exposed in the above getters/setters.

But the setters can be used to break the invariant -- something I
associate with getters/setters. (Unless setLow() throws, but that
is probably not a good idea.)

Or setLow could (perversely) also move High as needed to preserve the
distance invariant. Who knows? There isn't a setHigh anyway.

How about:

void Range::include(int n); // widen range to include 'n'
// can't come up with an interface for shrinking it

(Of course, this is just an example, and we don't know what
it is supposed to be used for.)

No, that's most often the problem with made-up examples. :-)

Bo Persson