From: Jani Nikula Date: Mon, 9 Apr 2012 21:31:34 +0000 (+0300) Subject: Re: [PATCH 4/4] Explicitly type void* pointers X-Git-Url: http://git.tremily.us/gitweb.cgi?a=commitdiff_plain;h=d66cb298a1029f99e049e1dd7fa625e804e98c96;p=notmuch-archives.git Re: [PATCH 4/4] Explicitly type void* pointers --- diff --git a/29/e8341f3a61fb4f597f679757d93f98d5cb328d b/29/e8341f3a61fb4f597f679757d93f98d5cb328d new file mode 100644 index 000000000..5665587b9 --- /dev/null +++ b/29/e8341f3a61fb4f597f679757d93f98d5cb328d @@ -0,0 +1,160 @@ +Return-Path: +X-Original-To: notmuch@notmuchmail.org +Delivered-To: notmuch@notmuchmail.org +Received: from localhost (localhost [127.0.0.1]) + by olra.theworths.org (Postfix) with ESMTP id D77514041CF + for ; Mon, 9 Apr 2012 14:31:42 -0700 (PDT) +X-Virus-Scanned: Debian amavisd-new at olra.theworths.org +X-Spam-Flag: NO +X-Spam-Score: -0.7 +X-Spam-Level: +X-Spam-Status: No, score=-0.7 tagged_above=-999 required=5 + tests=[RCVD_IN_DNSWL_LOW=-0.7] autolearn=disabled +Received: from olra.theworths.org ([127.0.0.1]) + by localhost (olra.theworths.org [127.0.0.1]) (amavisd-new, port 10024) + with ESMTP id p27yqgte60DQ for ; + Mon, 9 Apr 2012 14:31:42 -0700 (PDT) +Received: from mail-lpp01m010-f53.google.com (mail-lpp01m010-f53.google.com + [209.85.215.53]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) + (No client certificate requested) + by olra.theworths.org (Postfix) with ESMTPS id D49B84041C4 + for ; Mon, 9 Apr 2012 14:31:41 -0700 (PDT) +Received: by lahc1 with SMTP id c1so3966278lah.26 + for ; Mon, 09 Apr 2012 14:31:38 -0700 (PDT) +X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; + d=google.com; s=20120113; + h=from:to:subject:in-reply-to:references:date:message-id:mime-version + :content-type:x-gm-message-state; + bh=AY7koQTds8NWhz9uJK02k6P8bSg/aP55lxA8gPkTKe4=; + b=PfMHwIrWncbgpqnmsXZ9pzSFQevk2TuucYF6lBvbFxcjg4bijeQ6uf3ow9i8/3MBOD + iKhIGRQ97UqYrts56RqWAPSAzpaHTwSmlw8QthtwpeEiCkRKR0mrOGBL4nLeYjMKBG2S + q/vtLdVyPq0AHSqqXcQA72OcofHdclLonbOa1JtoyLsvi+qUO7f/k37lDsaJiHCdkbYm + TFazyXgxFdKqrN869Yiw+3blnH7eBHzKEEr4ORhuU0/ZaLu1JDGpSTprluFirfbT0i8T + f7de+w6qfdmoty/y0ddw34qUwj4xTQn64lRL5jIOJji3XSRq80NaXVb3eRfxJceGMlwC + Bujg== +Received: by 10.152.125.41 with SMTP id mn9mr13092580lab.30.1334007098775; + Mon, 09 Apr 2012 14:31:38 -0700 (PDT) +Received: from localhost (dsl-hkibrasgw4-fe50dc00-68.dhcp.inet.fi. + [80.220.80.68]) + by mx.google.com with ESMTPS id u4sm17074007lad.5.2012.04.09.14.31.36 + (version=SSLv3 cipher=OTHER); Mon, 09 Apr 2012 14:31:37 -0700 (PDT) +From: Jani Nikula +To: Vladimir Marek , + Notmuch Mail +Subject: Re: [PATCH 4/4] Explicitly type void* pointers +In-Reply-To: <20120409181543.GC10554@pub.czech.sun.com> +References: <1333966665-10469-1-git-send-email-Vladimir.Marek@oracle.com> + <1333966665-10469-5-git-send-email-Vladimir.Marek@oracle.com> + + <20120409181543.GC10554@pub.czech.sun.com>User-Agent: + Notmuch/0.12+81~g839a805 (http://notmuchmail.org) Emacs/23.3.1 + (i686-pc-linux-gnu) +Date: Tue, 10 Apr 2012 00:31:34 +0300 +Message-ID: <87mx6ka8y1.fsf@nikula.org> +MIME-Version: 1.0 +Content-Type: text/plain; charset=us-ascii +X-Gm-Message-State: + ALoCoQnwprzR8WVSMLExIIU3AmRHsiK8Zh3/rUo+S+L15VPsqqP3Qjz2vaOOwAdsYVGbT5VgzRV7 +X-BeenThere: notmuch@notmuchmail.org +X-Mailman-Version: 2.1.13 +Precedence: list +List-Id: "Use and development of the notmuch mail system." + +List-Unsubscribe: , + +List-Archive: +List-Post: +List-Help: +List-Subscribe: , + +X-List-Received-Date: Mon, 09 Apr 2012 21:31:43 -0000 + +Vladimir Marek 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 ++T *notmuch_talloc_steal(const void *new_ctx, const T *ptr) ++{ ++ return static_cast(talloc_steal(new_ctx, ptr)); ++} ++#undef talloc_steal ++#define talloc_steal notmuch_talloc_steal ++#endif ++#endif ++ + #endif