Cheers, mate!

That solves my issue (but with small fix).
/do_unpack[postfuncs] += "do_latest_link"
/instead/
//do_unpack[postfuncs] += "latest_link"

Because, without "do_" it says
WARNING: Function latest_link doesn't exist

/Here is the whole bbclass/:
/

    DESCRIPTION = "Creates symlink to the latest version workdir of the
    package"

    do_latest_link() {
         if [ -n "${WORKDIR}" ]; then
             linkname="$(dirname ${WORKDIR})/latest"
             rm -f $linkname
             ln -s $(basename ${WORKDIR}) $linkname
         fi
    }
    addtask latest_link after do_unpack

    do_unpack[postfuncs] += "do_latest_link"


But for better understanding I made the more throughout look into the 
documentations. I found the information about "postfuncs" you talk about 
[1]. However, the tasks description [2] doesn't say anything about 
including the task in the process, it just describes the demanded order 
that the task is put ( addtask something after|before othertask ).

That is so, until I read "3.6. Variable Flags"  [3]. Where is quite 
clearly stated those variables control functionality and *dependencies*.
The documentation is quite unclear in that case.

[1] 
http://www.yoctoproject.org/docs/current/bitbake-user-manual/bitbake-user-manual.html#executing-tasks
[2] 
http://www.yoctoproject.org/docs/current/bitbake-user-manual/bitbake-user-manual.html#tasks
[3] 
http://www.yoctoproject.org/docs/current/bitbake-user-manual/bitbake-user-manual.html#variable-flags 


Kind regards,
Bartosz Woronicz
Engineer, Software Configuration (SCM)
NSN - PL/Wroclaw

On 09.02.2016 10:10, EXT Burton, Ross wrote:
>
> On 9 February 2016 at 08:37, Woronicz, Bartosz ( NSN - PL/Wroclaw) 
> <bartosz.woronicz@nokia.com <mailto:bartosz.woronicz@nokia.com>> wrote:
>
>     Ok, but I don't want to run it everytime, just after the
>     do_unpack. What I need to put it in requirements for each recipe ?
>     Maybe something like
>
>     do_unpack[require] = "latest_link"
>
>
> do_unpack[postfuncs] += "latest_link" will run latest_link after 
> unpack has executed.
>
> Ross