[Qt-creator] Use #pragma once as default instead of header guards

[Bubke Marco]

We support it but it will be slow. It is your decision. Anyway how often do you need code completion in the header file. 

Maybe we can fix it in the future but it depends on Clang.

Anyway I don't want to force you to anything. It was about the future. So #pragma once would be allowed for the people who want to use it.

________________________________________
From: Qt-creator <qt-creator-bounces at qt-project.org> on behalf of Christian Kandeler <christian.kandeler at theqtcompany.com>
Sent: Wednesday, January 13, 2016 12:29 PM
To: qt-creator at qt-project.org
Subject: Re: [Qt-creator] Use #pragma once as default instead of header guards

On 01/13/2016 11:55 AM, Bubke Marco wrote:
> Hello
>
> With the clang code model there is a problem to generate a preamble file with header guards. Imaging a preamble file is like a automatically pre compiled header for the include block at the top. But there are limitations. One is that every ifndef has to match is #endif inside of the preamble but this not the case for header guards.
>
> #ifndef HEADER_GUARD
> #define HEADER_GUARD
> #include <QtGui> // this would be compiled in the preamble once
>
> void foo()
> {
>     auto bahn = nullptr;
> }
>
>
> #endif
>
> We don't generate a preamble for this case because the opening ifndefs is not matching the endif. In that case the clang model will be very slow!
>
> So I propose we change our wizards to utilize #pragma once and use it for every new file. We can change header files where we need code completion on demand too.

Unless I'm misunderstanding the point, you seem to suggest that people
change their (non-broken) projects to work around problems in Creator's
code model. This cannot possibly be the solution, can it? The code model
needs to support users' code, not the other way around.


Christian
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