programming guidelines, prefer free functions

From: jsiek_at_[hidden]
Date: 2000-08-17 10:14:19

I have a suggestion for the boost programming guidelines.  As various
boost members have pointed out in the past (most recently Dave), it is
better to use free (non-member) functions over member functions in
public interfaces.

The rationale for this is that free functions allow for what I call
"external adaptation" (does anyone have a different name for this?).
Suppose you have a third party component (TPC) that you want to use,
but it doesn't match the interface needed for your softare. You don't
have access to the source code, so you can't change the TPC. If your
interface consists of member functions, you've only got one choice,
create a wrapper class for the TPC. Wrapper classes are difficult to
use and error prone. You have to be sure to implement the constructors
and destructors properly, and may have to write a bunch of delegating
functions. Also, every time a TPC object enters your code, you have to
wrap the object. On the other hand, if your interface consists only of
free functions, all you have to do is create specializations of these
functions for the TPC. Then you can use the TPC directly in your code.
Much simpler!

One possible complaint is that free functions rule out using dynamic
dispatch (virtual functions). On the contrary, simply specialize the
free function in terms of the abstract base class, and write a
one-liner that dispatches to the virtual function.

Cheers,

Jeremy