[Development] #pragma once

[Ville Voutilainen]

On 24 January 2018 at 12:34, Mitch Curtis <mitch.curtis at qt.io> wrote:
>
>
>> -----Original Message-----
>> From: Ville Voutilainen [mailto:ville.voutilainen at gmail.com]
>> Sent: Wednesday, 24 January 2018 11:25 AM
>> To: Alexander Nassian <nassian at bitshift-dynamics.com>
>> Cc: Mitch Curtis <mitch.curtis at qt.io>; development at qt-project.org
>> Subject: Re: [Development] #pragma once
>>
>> On 24 January 2018 at 12:22, Alexander Nassian <nassian at bitshift-
>> dynamics.com> wrote:
>> > Maybe because it’s not part of the C++ standard?
>>
>> #pragma once is not a replacement for include guards.
>
> Why not?
>
>> It's not part of the C++ standard because it doesn't always work
>
> In which ways? My quick search gave me these:
>
> https://stackoverflow.com/a/1946730/904422
> https://en.wikipedia.org/wiki/Pragma_once#Caveats

That wikipedia link seems to describe the problems fairly accurately.

>> and modules are a superior solution anyway.
> How so?

Because you can import the same module multiple times without concerns
about re-definitions,
and that import is much faster than parsing a header file.