draft proposal for ref counting in D

Walter Bright newshound2 at digitalmars.com
Wed Oct 9 19:23:18 PDT 2013


Looks like this should go into the O-C DIP.


On 6/29/2013 5:38 AM, Michel Fortin wrote:
 >
 > Implementing ARC for Objective-C is going to require some more compiler 
support anyway (for autoreleased objects notably). Tweaking the compiler it so 
accepts Objective-C interfaces should just be a matter of tweaking the boolean 
expression that makes this check. "if (classdelc->objc && interfacedecl->objc) 
return true;" or something like that.
 >
 > As for which function the compiler should call, it'll probably need to be 
special-cased for Objective-C in the compiler too. Here's the list of changes 
that'd be needed for Objective-C ARC:
 >
 > == Retain ==
 > COM:  if (obj) obj->AddRef();
 > ObjC: obj = objc_retain(obj);
 > ObjC blocks: obj = objc_retainBlock(obj); // objc_retainBlock might do a copy
 >
 > == Release ==
 > COM:  if (obj) obj->Release();
 > ObjC: objc_release(obj);
 >
 > == Assignment ==
 > COM:  if (obj) obj->AddRef(); if (var) var->Release(); var = obj;
 > ObjC: objc_storeStrong(&var, obj);
 > ObjC blocks: obj = objc_retainBlock(obj); objc_release(var); var = obj;
 >
 > As long as Walter implements D ARC in a way we can make the above 
substitutions it shouldn't be too hard.
 >
 > Then, support for autorelease is a matter of calling objc_autorelease on 
returned objects from autoreleasing functions, followed by objc_retain after the 
function call in the caller. We'll also have to check what ObjC ARC does for 
pointer write-backs to autoreleased variables and mimick that.
 >
 > There's an optimized path for autoreleased return values that we should use, 
but I'd defer that to later. It involves a special no-op instruction to insert 
at the right place as a flag. Also, autoreleased returns should be eliminated 
when inlining.
 >


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