draft proposal for ref counting in D

[Walter Bright]

Michel Fortin wrote:

Le 26-juin-2013 à 19:48, Walter Bright  a écrit :

 > D (like C and C++) loves to manipulate pointers. Having to call a function 
every time this is done would be a disaster. It means that people would be 
motivated to drop down to C to do the fast code, and we might as well throw in 
the towel.

But at the same time, having a GC that stops the world at irregular interval is 
worse for certain kind of things, games notably. It's been stated often on the 
forum that game developers prefer increasing the overhead if it prevents those 
hiccups. Making everything in D reference-counted would undoubtedly increase the 
general overhead, but it'd allow game developers to leverage the whole language 
and its libraries instead of restricting themselves to a custom subset of the 
class hierarchy derived from a reference counted class.

And about pointer manipulation: for cases where you know for certain that the 
pointer still points to the same memory block before and after the assignment 
(when you call popFront on an array for instance), you have no reference count 
to update and can elide the call.

The downside of optional support for language-wide reference counting is that it 
requires two incompatible codegen (or rather one incompatible with RC). We could 
have only one if it's the one that calls the retain/release functions on pointer 
assignment, with those functions replaced with empty stubs in druntime when 
reference counting is disabled, but some overhead would remain for the function 
call.

I'm not claiming this is the right solution. It's just an idea I wanted to 
mention as an aside because it has some common points. It is however a mostly 
separate matter from your initial goal of supporting custom reference counting 
schemes for some object hierarchies. I decided to write about it mostly because 
you talked about reimplementing arrays using classes and that got me thinking. 
But perhaps I shouldn't have mentioned it because it seems to be side-tracking 
the discussion.