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+From: Jani Nikula <jani@nikula.org>\r
+To: Vladimir Marek <Vladimir.Marek@Oracle.COM>,\r
+ Notmuch Mail <notmuch@notmuchmail.org>\r
+Subject: Re: [PATCH 4/4] Explicitly type void* pointers\r
+In-Reply-To: <20120409181543.GC10554@pub.czech.sun.com>\r
+References: <1333966665-10469-1-git-send-email-Vladimir.Marek@oracle.com>\r
+ <1333966665-10469-5-git-send-email-Vladimir.Marek@oracle.com>\r
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+ <20120409181543.GC10554@pub.czech.sun.com>User-Agent:\r
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+Date: Tue, 10 Apr 2012 00:31:34 +0300\r
+Message-ID: <87mx6ka8y1.fsf@nikula.org>\r
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+\r
+Vladimir Marek <Vladimir.Marek@Oracle.COM> writes:\r
+\r
+> Hi,\r
+>\r
+>> Hi, does notmuch not compile without this? IIRC talloc_steal is a macro\r
+>> that's supposed to provide type safety (at least with GCC), and I'd be\r
+>> hesitant about adding the casts. Please look in your talloc.h.\r
+>\r
+> It does not compile. It might be that I'm using Sun/Oracle CC instead of\r
+> gcc. The error looks like this:\r
+>\r
+> "lib/database.cc", line 1368: Error: Cannot assign void* to const char*.\r
+\r
+In general, that's not a difference in the C++ compilers. You can't\r
+assign 'void *' to 'T *' in C++.\r
+\r
+> When looking into talloc documentation, the definition seems to be:\r
+>\r
+> void* talloc_steal ( const void * new_ctx, const void * ptr )\r
+>\r
+> http://talloc.samba.org/talloc/doc/html/group__talloc.html#gaccc66139273e727183fb5bdda11ef82c\r
+>\r
+>\r
+> When looking into talloc.h, it says:\r
+>\r
+> /* try to make talloc_set_destructor() and talloc_steal() type safe,\r
+> if we have a recent gcc */\r
+\r
+It just so happens that the trick for type safety fixes the problem for\r
+recent GCC by having an explicit cast.\r
+\r
+> So, maybe the way to satisfy everyone would be:\r
+>\r
+> notmuch_message_t *tmp_message = message;\r
+> talloc_steal(notmuch, tmp_message);\r
+> return(tmp_message);\r
+>\r
+> Or alternatively,\r
+>\r
+> #if (__GNUC__ >= 3)\r
+> return talloc_steal (notmuch, message);\r
+> #else\r
+> return (notmuch_message_t*) talloc_steal (notmuch, message);\r
+> #fi\r
+>\r
+>\r
+> Of course I'm happy either way :)\r
+\r
+I'm throwing in a third alternative below. Does it work for you? I think\r
+it's both prettier and uglier than the above at the same time! ;)\r
+\r
+A middle ground would be to change the callers to use\r
+"notmuch_talloc_steal", and just #define notmuch_talloc_steal\r
+talloc_steal if __GNUC__ >= 3.\r
+\r
+One could argue upstream talloc should have this, but OTOH it's a C\r
+library.\r
+\r
+BR,\r
+Jani.\r
+\r
+\r
+diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h\r
+index ea836f7..83b46e8 100644\r
+--- a/lib/notmuch-private.h\r
++++ b/lib/notmuch-private.h\r
+@@ -499,4 +499,22 @@ _notmuch_filenames_create (const void *ctx,\r
+ \r
+ NOTMUCH_END_DECLS\r
+ \r
++#ifdef __cplusplus\r
++/* Implicit typecast from 'void *' to 'T *' is okay in C, but not in\r
++ * C++. In talloc_steal, an explicit cast is provided for type safety\r
++ * in some GCC versions. Otherwise, a cast is required. Provide a\r
++ * template function for this to maintain type safety, and redefine\r
++ * talloc_steal to use it.\r
++ */\r
++#if !(__GNUC__ >= 3)\r
++template <class T>\r
++T *notmuch_talloc_steal(const void *new_ctx, const T *ptr)\r
++{\r
++ return static_cast<T*>(talloc_steal(new_ctx, ptr));\r
++}\r
++#undef talloc_steal\r
++#define talloc_steal notmuch_talloc_steal\r
++#endif\r
++#endif\r
++\r
+ #endif\r
projects / notmuch-archives.git / commitdiff