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40 (version=SSLv3 cipher=OTHER); Mon, 09 Apr 2012 14:31:37 -0700 (PDT)
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41 From: Jani Nikula <jani@nikula.org>
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42 To: Vladimir Marek <Vladimir.Marek@Oracle.COM>,
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43 Notmuch Mail <notmuch@notmuchmail.org>
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44 Subject: Re: [PATCH 4/4] Explicitly type void* pointers
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45 In-Reply-To: <20120409181543.GC10554@pub.czech.sun.com>
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46 References: <1333966665-10469-1-git-send-email-Vladimir.Marek@oracle.com>
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47 <1333966665-10469-5-git-send-email-Vladimir.Marek@oracle.com>
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48 <CAB+hUn_QyMAfC1-Dr23T63ObX=cwuBOzcyCi=61w0MtGRMyt2w@mail.gmail.com>
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49 <20120409181543.GC10554@pub.czech.sun.com>User-Agent:
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50 Notmuch/0.12+81~g839a805 (http://notmuchmail.org) Emacs/23.3.1
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52 Date: Tue, 10 Apr 2012 00:31:34 +0300
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72 Vladimir Marek <Vladimir.Marek@Oracle.COM> writes:
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76 >> Hi, does notmuch not compile without this? IIRC talloc_steal is a macro
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77 >> that's supposed to provide type safety (at least with GCC), and I'd be
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78 >> hesitant about adding the casts. Please look in your talloc.h.
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80 > It does not compile. It might be that I'm using Sun/Oracle CC instead of
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81 > gcc. The error looks like this:
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83 > "lib/database.cc", line 1368: Error: Cannot assign void* to const char*.
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85 In general, that's not a difference in the C++ compilers. You can't
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86 assign 'void *' to 'T *' in C++.
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88 > When looking into talloc documentation, the definition seems to be:
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90 > void* talloc_steal ( const void * new_ctx, const void * ptr )
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92 > http://talloc.samba.org/talloc/doc/html/group__talloc.html#gaccc66139273e727183fb5bdda11ef82c
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95 > When looking into talloc.h, it says:
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97 > /* try to make talloc_set_destructor() and talloc_steal() type safe,
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98 > if we have a recent gcc */
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100 It just so happens that the trick for type safety fixes the problem for
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101 recent GCC by having an explicit cast.
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103 > So, maybe the way to satisfy everyone would be:
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105 > notmuch_message_t *tmp_message = message;
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106 > talloc_steal(notmuch, tmp_message);
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107 > return(tmp_message);
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109 > Or alternatively,
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111 > #if (__GNUC__ >= 3)
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112 > return talloc_steal (notmuch, message);
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114 > return (notmuch_message_t*) talloc_steal (notmuch, message);
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118 > Of course I'm happy either way :)
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120 I'm throwing in a third alternative below. Does it work for you? I think
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121 it's both prettier and uglier than the above at the same time! ;)
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123 A middle ground would be to change the callers to use
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124 "notmuch_talloc_steal", and just #define notmuch_talloc_steal
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125 talloc_steal if __GNUC__ >= 3.
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127 One could argue upstream talloc should have this, but OTOH it's a C
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134 diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
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135 index ea836f7..83b46e8 100644
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136 --- a/lib/notmuch-private.h
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137 +++ b/lib/notmuch-private.h
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138 @@ -499,4 +499,22 @@ _notmuch_filenames_create (const void *ctx,
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142 +#ifdef __cplusplus
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143 +/* Implicit typecast from 'void *' to 'T *' is okay in C, but not in
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144 + * C++. In talloc_steal, an explicit cast is provided for type safety
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145 + * in some GCC versions. Otherwise, a cast is required. Provide a
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146 + * template function for this to maintain type safety, and redefine
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147 + * talloc_steal to use it.
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149 +#if !(__GNUC__ >= 3)
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150 +template <class T>
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151 +T *notmuch_talloc_steal(const void *new_ctx, const T *ptr)
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153 + return static_cast<T*>(talloc_steal(new_ctx, ptr));
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155 +#undef talloc_steal
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156 +#define talloc_steal notmuch_talloc_steal
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