Free functions versus member functions

[Walter Bright]

Continuing the discussion from the thread "questions on PhanTango 'merger'":

Lars Ivar Igesund wrote:
 > It is not as if such functions are non-existant in Tango, so which exact
 > functionality do you think is better expressed through free standing
 > functions rather than objects? The answers of others shows that this
 > usually is wanted for objects where you often need only one operation on
 > the given object, even if others are available. This don't remove the 
fact
 > that an object (class) equally often is a useful abstraction, and 
when that
 > is established, free standing functions usually should be implemented as
 > wrappers around each method on the object, rather than the object being
 > implemented via free standing functions. This is why Tango looks as 
it does
 > today; we have avoided wrappers of our own code if possible, because they
 > degrade orthogonality of the API, and add more code to maintain. 
Whether we
 > have been to strict in enforcing that stance, is an open question.

I've been stumped by this design issue before. Should functionality be 
done as a set of free functions, or as member functions? I remember 
going over this with Matthew Wilson, and he resolved it by implementing 
two parallel sets of interfaces: one free, the other member. I thought 
that doing both was a copout, but couldn't figure out which one was right.

I eventually ran across this article by Scott Meyers 
http://www.ddj.com/cpp/184401197
which made a lot of sense. It gives some good guidelines to use to make 
such decisions, and backs it up with reasoning that I find compelling.

Isn't it funny how we've completed the circle? We went from all free 
functions in C, to all member functions in C++, and now back to free 
functions? <g>