From: Tomi Ollila <tomi.ollila@iki.fi>
To: Charlie Allom <charlie@mediasp.com>, notmuch@notmuchmail.org,
	Ali Polatel <alip@exherbo.org>
Subject: Re: [PATCH] ruby: extern values in ruby defs.h
In-Reply-To: <1336481467-66356-1-git-send-email-charlie@mediasp.com>
References: <1336481467-66356-1-git-send-email-charlie@mediasp.com>
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	(x86_64-unknown-linux-gnu)
Date: Tue, 08 May 2012 23:13:28 +0300
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On Tue, May 08 2012, Charlie Allom <charlie@mediasp.com> wrote:

> Currently, building on OSX complains about linking duplicate symbols. This
> fixes the error.
> ---

I just spent some time looking out this declaration/definition thing --
it is not easy to find proper documentation...

Finally, I was reading this:

http://www.open-std.org/jtc1/sc22/wg14/www/docs/C99RationaleV5.10.pdf

(warning (goatse class), pdf converted from word document ;)

At the end of page 33 is interesting (also beginning of 34 and it is good
to start from middle of page 32)

Those mention 4 different way 'external linkage' is handled in pre-89
compilers...

Standards-compliant (c99, at least) compilers should handle this is 
a combination of 'Strict Ref/Def' and 'Initialization' model. IIUC this
means that if variable is defined (I mean declared) as

int i;

It is a tentative definition; There can be many of these seen by c compiler
while compiling c files and when linking is done there will be one storage
allocated for this variable. There can be (at most) one definition like

int i = 0; 

in source code, even another 'int i = 0;' is not allowed according to
the standard -- some compilers may make this work (and even the case where
there is 'int i = 1;')

But, there are also compilers that only allow 'Strict Ref/Def' model; IIUC
then there can be only one 'int i;' (or 'int i = 0;') -- and all others
(declarations) needs to be in format 'extern int i;'. The 'Strict Ref/Def'
model is the model specified in K&R.

All of that said, LGTM!

Tomi

>  bindings/ruby/defs.h |   46 +++++++++++++++++++++++-----------------------
>  1 files changed, 23 insertions(+), 23 deletions(-)
>
> diff --git a/bindings/ruby/defs.h b/bindings/ruby/defs.h
> index 81f652f..bd124cc 100644
> --- a/bindings/ruby/defs.h
> +++ b/bindings/ruby/defs.h
> @@ -24,31 +24,31 @@
>  #include <notmuch.h>
>  #include <ruby.h>
>
> -VALUE notmuch_rb_cDatabase;
> -VALUE notmuch_rb_cDirectory;
> -VALUE notmuch_rb_cFileNames;
> -VALUE notmuch_rb_cQuery;
> -VALUE notmuch_rb_cThreads;
> -VALUE notmuch_rb_cThread;
> -VALUE notmuch_rb_cMessages;
> -VALUE notmuch_rb_cMessage;
> -VALUE notmuch_rb_cTags;
> -
> -VALUE notmuch_rb_eBaseError;
> -VALUE notmuch_rb_eDatabaseError;
> -VALUE notmuch_rb_eMemoryError;
> -VALUE notmuch_rb_eReadOnlyError;
> -VALUE notmuch_rb_eXapianError;
> -VALUE notmuch_rb_eFileError;
> -VALUE notmuch_rb_eFileNotEmailError;
> -VALUE notmuch_rb_eNullPointerError;
> -VALUE notmuch_rb_eTagTooLongError;
> -VALUE notmuch_rb_eUnbalancedFreezeThawError;
> -VALUE notmuch_rb_eUnbalancedAtomicError;
> -
> -ID ID_call;
> -ID ID_db_create;
> -ID ID_db_mode;
> +extern VALUE notmuch_rb_cDatabase;
> +extern VALUE notmuch_rb_cDirectory;
> +extern VALUE notmuch_rb_cFileNames;
> +extern VALUE notmuch_rb_cQuery;
> +extern VALUE notmuch_rb_cThreads;
> +extern VALUE notmuch_rb_cThread;
> +extern VALUE notmuch_rb_cMessages;
> +extern VALUE notmuch_rb_cMessage;
> +extern VALUE notmuch_rb_cTags;
> +
> +extern VALUE notmuch_rb_eBaseError;
> +extern VALUE notmuch_rb_eDatabaseError;
> +extern VALUE notmuch_rb_eMemoryError;
> +extern VALUE notmuch_rb_eReadOnlyError;
> +extern VALUE notmuch_rb_eXapianError;
> +extern VALUE notmuch_rb_eFileError;
> +extern VALUE notmuch_rb_eFileNotEmailError;
> +extern VALUE notmuch_rb_eNullPointerError;
> +extern VALUE notmuch_rb_eTagTooLongError;
> +extern VALUE notmuch_rb_eUnbalancedFreezeThawError;
> +extern VALUE notmuch_rb_eUnbalancedAtomicError;
> +
> +extern ID ID_call;
> +extern ID ID_db_create;
> +extern ID ID_db_mode;
>
>  /* RSTRING_PTR() is new in ruby-1.9 */
>  #if !defined(RSTRING_PTR)
> --
> 1.7.5.4
>
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