Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 1 Sep 2009 13:02:48 -0500

On Tuesday 01 September 2009 10:25:23 Jeff Hill wrote:
>
> The controversy arises, of course, surrounding
> changing the gdd interface which is in use.

My suggestion (as a complete outsider, I have never had to write code that 
uses GDDs, so feel free to completely ignore me) was to not change the GDD 
API at all (since doing so would break existing code) and instead to swallow 
the awkward GDD behavior in the smartGDDPointer.

> Unfortunately, unless one removes referencing, and also new, from the gdd
> interface, then this still does not prevent someone from inadvertently
> doing this. This type of unfortunate pitfall is what Alex and others have
> experienced - and complained about.
> 
> gdd * pGDD = new gdd();
> ...
> smartGDDPointer pDD1;	// Empty
> pDD1.newGdd(); //create 1st one
> ...
> smartGDDPointer pDD1 = pGDD; // replace with 2nd, woops forgot to call
> pGDD->unreferenced()

But in that example, the user is still using a gdd* and calling new gdd(), 
whereas they should probably make pGDD a smartGDDPointer too, at which point 
the bug disappears.

There may be places where you might still want/need to use gdd* pointers, but 
but hopefully they can be minimized.

> BTW: Is there a reason why you have a preference:
> // this
> smartGDDPointer pDD1;	// Empty
> pDD1.newGdd();		// Create one
> // versus this (what I would probably implement lacking further input)
> smartGDDPointer pDD1 = gdd :: factory (); // Create one
>
> A messy aspect of factories is that one must replicate all of the various
> ctor signatures for the various modes of the target. I think that there are
> six of them with gdd. Maybe not so bad.

I was trying to avoid changing the GDD API; given that it has existing users 
and a limited lifetime it's probably a bad idea to force them to change their 
code now (since you're going to be doing that anyway when DA comes in), so 
you would have to leave the existing constructors in place.  I thought it 
would be better to extend the smartGDDPointer API, since it's already 
gdd-specific and that's where you're trying to encourage people to go anyway.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harold Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System