[CMake] Newbie question: Static linking

[Michael Jackson]

You might want to take a look at the Factory design pattern.

-----
Mike Jackson                     www.bluequartz.net
Principal Software Engineer       mike.jackson at bluequartz.net
BlueQuartz Software               Dayton, Ohio
Sent from my mobile device.

On May 23, 2011, at 5:51, Sanatan Rai <sanatan at gmail.com> wrote:

> On 23 May 2011 10:18, Michael Wild <themiwi at gmail.com> wrote:
>> On 05/23/2011 10:23 AM, Hendrik Sattler wrote:
>>> Zitat von Sanatan Rai <sanatan at gmail.com>:
>>>> The `global initialisation' stuff is just the following pattern:
>>>>
>>>> namespace {
>>>>   helper1 *helper1Creator()
>>>>   {
>>>>     return (new helper1());
>>>>   }
>>>>   const bool helper1Registered = factory::instance().registerhelper
>>>>     ("helper1", helper1Creator);
>>>> }
>>>>
>>>> So when I put the helpers in a separate library, these lines are not
>>>> called.
>>>
>>> Then you don't understand the implications of static libraries, yet.
>>> Use the following from "man ld":
>>>  --whole-archive
>>>        For    each  archive  mentioned  on  the  command  line   after the
>>>        --whole-archive option, include every object file in the archive in
>>>        the link, rather than searching the archive for the required object
>>>        files.  This is normally used to turn an archive file into a shared
>>>        library, forcing every object  to  be  included  in    the
> <snipped>
>
> Thanks Hendrik, that works! For the record, I have added the following:
>
> target_link_libraries(myTarget
>    "-Wl,-whole-archive -L./helpers -lhelper1 -Wl,-no-whole-archive"
>    "-Wl,-whole-archive -L./helpers -lhelper2 -Wl,-no-whole-archive")
>
> I am not happy about having to provide the search path explicitely, but hey.
>
>> But this will only work when using GNU ld (or compatible). AFAIK the
>> linker on APPLE uses a different option, and MSVC doesn't have an
>> equivalent at all (you can only specify individual symbols that should
>> be linked forcibly).
>>
>> The real solution is to ditch this whole idea of global, static
>> initialization objects. It's usually a very bad solution, leading to all
>> kinds of non-deterministic behavior. You'll be much better off with an
>> explicit registration scheme.
>>
>> My 2c.
>>
>> Michael
>
> I couldn't agree more. However, there does not appear to be an alternative
> way of doing this registration. Briefly, here is the problem I am
> trying to solve.
>
>  * I have a base class (say) myBase.
>  * I expect other users of my library to derive objects from myBase.
>  * The application `creates' the derived objects as per the pattern above,
>    based on which ones the user wants as per a config file.
> * So: if the user specifies an object that is not built, then the app
> is going to
>   throw an exception and abort.
> * The whole point of doing this is that the application is a
> `framework' for the
>   user `to host his derived class'.
>
> This approach permits me to keep the application and the `framework' code
> agnostic to the user's derived classes.
>
> I'd be more than happy to find a better way of achieving the
> framework's agnosticism
> to the derived classes, while providing the user to derive whatever
> objects he likes.
>
> When I solved this problem on .NET I was forced to run through all the
> assemblies
> to find the relevant objects and then use reflection to instantiate
> them. That was even
> uglier.
>
> Thanks all!
>
> --Sanatan
> --
> Sanatan Rai
> 3, Admirals Court,
> 30, Horselydown Lane,
> London, SE1 2LJ.
> +44-20-7403-2479.
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