[Interest] Qt 5.5.x

[Bo Thorsen]

Den 12-09-2015 kl. 10:19 skrev Till Oliver Knoll:
>
> Am 11.09.2015 um 19:59 schrieb Matthew Woehlke <mwoehlke.floss at gmail.com
> <mailto:mwoehlke.floss at gmail.com>>:
>
>> On 2015-09-11 13:41, Till Oliver Knoll wrote:
>>> You can further reduce the "dependency tree" of your sources by
>>> making use of the private "d-pointer" pattern (there is a name for
>>> it which currently escapes me)
>>
>> PIMPL? ;-)
>>
>> https://en.wikipedia.org/wiki/Pimpl
>
> Exactly :) Even though I had the term "Cheshire Cat" in mind :) (I yet
> have to google why that pattern is named after a cat).
>
> But while we're there, quoting from that article:
>
> "One type of opaque pointer commonly used in C++ class declarations is
> the d-pointer. The d-pointer is the only private data member of the
> class and points to an instance of a struct. Named by Arnt Gulbrandsen
> <https://en.m.wikipedia.org/w/index.php?title=Arnt_Gulbrandsen&action=edit&redlink=1> of
> Trolltech <https://en.m.wikipedia.org/wiki/Trolltech>, this method
> allows class declarations to omit private data members, except for the
> d-pointer itself.^[6]
> <https://en.m.wikipedia.org/wiki/Pimpl#cite_note-6>  The result: (a)
> more of the class implementation is hidden from view; (b) adding new
> data members to the private struct does not affect binary compatibility;
> (c) the header file containing the class declaration only needs to
> #include those other files needed for the class interface, rather than
> for its implementation. One side benefit is that compilations are faster
> because the header file changes less often. The d-pointer is heavily
> used in the Qt <https://en.m.wikipedia.org/wiki/Qt_(toolkit)> and KDE
> <https://en.m.wikipedia.org/wiki/KDE> libraries."

There is another term used for it as well: Compiler firewall. The 
d-pointers make it impossible for the compiler to perform a long list of 
optimizations.

I value using d-pointers over raw speed for most cases. But it's one 
thing to keep in mind if you really have to optimize.

Bo Thorsen,
Director, Viking Software.

-- 
Viking Software
Qt and C++ developers for hire
http://www.vikingsoft.eu