From: Jani Nikula <jani@nikula.org>
To: Vladimir Marek <Vladimir.Marek@Oracle.COM>,
Notmuch Mail <notmuch@notmuchmail.org>
Subject: Re: [PATCH 4/4] Explicitly type void* pointers
Date: Tue, 10 Apr 2012 00:31:34 +0300 [thread overview]
Message-ID: <87mx6ka8y1.fsf@nikula.org> (raw)
In-Reply-To: <20120409181543.GC10554@pub.czech.sun.com>
Vladimir Marek <Vladimir.Marek@Oracle.COM> writes:
> Hi,
>
>> Hi, does notmuch not compile without this? IIRC talloc_steal is a macro
>> that's supposed to provide type safety (at least with GCC), and I'd be
>> hesitant about adding the casts. Please look in your talloc.h.
>
> It does not compile. It might be that I'm using Sun/Oracle CC instead of
> gcc. The error looks like this:
>
> "lib/database.cc", line 1368: Error: Cannot assign void* to const char*.
In general, that's not a difference in the C++ compilers. You can't
assign 'void *' to 'T *' in C++.
> When looking into talloc documentation, the definition seems to be:
>
> void* talloc_steal ( const void * new_ctx, const void * ptr )
>
> http://talloc.samba.org/talloc/doc/html/group__talloc.html#gaccc66139273e727183fb5bdda11ef82c
>
>
> When looking into talloc.h, it says:
>
> /* try to make talloc_set_destructor() and talloc_steal() type safe,
> if we have a recent gcc */
It just so happens that the trick for type safety fixes the problem for
recent GCC by having an explicit cast.
> So, maybe the way to satisfy everyone would be:
>
> notmuch_message_t *tmp_message = message;
> talloc_steal(notmuch, tmp_message);
> return(tmp_message);
>
> Or alternatively,
>
> #if (__GNUC__ >= 3)
> return talloc_steal (notmuch, message);
> #else
> return (notmuch_message_t*) talloc_steal (notmuch, message);
> #fi
>
>
> Of course I'm happy either way :)
I'm throwing in a third alternative below. Does it work for you? I think
it's both prettier and uglier than the above at the same time! ;)
A middle ground would be to change the callers to use
"notmuch_talloc_steal", and just #define notmuch_talloc_steal
talloc_steal if __GNUC__ >= 3.
One could argue upstream talloc should have this, but OTOH it's a C
library.
BR,
Jani.
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index ea836f7..83b46e8 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -499,4 +499,22 @@ _notmuch_filenames_create (const void *ctx,
NOTMUCH_END_DECLS
+#ifdef __cplusplus
+/* Implicit typecast from 'void *' to 'T *' is okay in C, but not in
+ * C++. In talloc_steal, an explicit cast is provided for type safety
+ * in some GCC versions. Otherwise, a cast is required. Provide a
+ * template function for this to maintain type safety, and redefine
+ * talloc_steal to use it.
+ */
+#if !(__GNUC__ >= 3)
+template <class T>
+T *notmuch_talloc_steal(const void *new_ctx, const T *ptr)
+{
+ return static_cast<T*>(talloc_steal(new_ctx, ptr));
+}
+#undef talloc_steal
+#define talloc_steal notmuch_talloc_steal
+#endif
+#endif
+
#endif
next prev parent reply other threads:[~2012-04-09 21:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-09 10:17 notmuch on Solaris Vladimir.Marek
2012-04-09 10:17 ` [PATCH 1/4] Make configure use /bin/bash instead of /bin/sh Vladimir.Marek
2012-04-09 11:10 ` Jani Nikula
2012-04-09 12:19 ` Vladimir Marek
2012-04-10 17:26 ` Tomi Ollila
2012-04-11 8:43 ` Vladimir Marek
2012-04-11 18:47 ` Tomi Ollila
2012-04-30 11:58 ` David Bremner
2012-04-30 12:09 ` Tomi Ollila
2012-04-09 10:17 ` [PATCH 2/4] dirent->d_type not available on Soalris Vladimir.Marek
2012-04-09 11:17 ` Jani Nikula
2012-04-09 15:12 ` Vladimir Marek
2012-04-09 15:46 ` Adam Wolfe Gordon
2012-04-09 16:32 ` Vladimir.Marek
2012-04-11 18:57 ` Tomi Ollila
2012-04-11 19:36 ` Austin Clements
2012-04-09 10:17 ` [PATCH 3/4] Private strsep implementation Vladimir.Marek
2012-10-15 5:05 ` Ethan Glasser-Camp
2012-04-09 10:17 ` [PATCH 4/4] Explicitly type void* pointers Vladimir.Marek
2012-04-09 11:04 ` Jani Nikula
2012-04-09 18:15 ` Vladimir Marek
2012-04-09 21:31 ` Jani Nikula [this message]
2012-04-10 6:53 ` Vladimir Marek
2012-04-11 21:11 ` Austin Clements
2012-04-12 8:02 ` Jani Nikula
2012-04-12 17:57 ` Austin Clements
2012-04-15 21:05 ` Jani Nikula
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