Hello Joost, Friday, November 19, 2010, 1:02:59 PM, you wrote:
JvdS> Well, this issue leaded to a large discussion elsewhere. I was wondering JvdS> when someone else would even notice this incompatibility. A lot of JvdS> alternatives have been discussed, but I coud not find any which is less JvdS> intrusive. I had followed the discussion in the public lists but not in the development internal lists. JvdS> In an nutshell: the behavior of 'const' parameters is undefined. When JvdS> using cdecl the 'const' keyword is simply ignored. But we do need to JvdS> pass the GUID by reference. I'm aware... JvdS> There are two options: JvdS> 1: Change the behavior of const-parameters. That can lead to JvdS> unpredictable problems which are not noticed by the compiler. It could JvdS> be an option to use some setting to define the behavior of 'const', but JvdS> in that case that setting have to be set for all units that do a call to JvdS> QueryInterface. (ie: all code using interfaces, so it means this setting JvdS> has to be set everywhere where COM code is used) Currently Win32 (only win32) could work with const in that interface, taking in account that any other interface functions in IUnknown descendents will be mostly typed with const instead constref, so people with interfaces will inadvertly have const everywhere but QueryInterface. Anyway, continue reading... JvdS> 2: Change the definition to constref, so the compiler will complain if a JvdS> user override the QueryInterface's definition, and can adapt the code. This is the best, of course, but is there any possibility to fine tune the message error in that case to offer the solution to the programmer directly ? Can a special error message be emited for this error in QueryInterface ? JvdS> Notice that until now I've only heard of code which overrides JvdS> QueryInterface in the Free Pascal code itself, in the Lazarus code, ZEOS JvdS> and the code from one commercial developer who also works on JvdS> Lazarus/Free Pascal. JvdS> It is an incompatibility, yes. But I think it's not too intrusive and I JvdS> see no alternatives... No, not intrusive, but very hard to find the solution for average joe, in fact I had solved it in my Zeos just after seen the "error" but most people are not aware of the change. I'm looking for a help in solution, not an interface change. -- Best regards, José _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
