[sr-dev] replacing k pvars with s selects

[Daniel-Constantin Mierla]

On 14.07.2009 15:54 Uhr, Jan Janak wrote:
> On Fri, Jul 3, 2009 at 6:45 PM, Daniel-Constantin
> Mierla<miconda at gmail.com> wrote:
>   
>>>  > whose confusion?
>>> like the discussion on lookup_domain function revealed, it is confusing
>>> that the same prefix ($ char) is used for two different things.
>>>
>>>       
>> from my point of view, all are script variables: avps, references to sip
>> message parts, etc ... therefore the have to start with same char, and most
>> of the programming languages use $ for that. It is what was decided long
>> time ago in openser when pseudo-variables were introduced in core.
>>     
>
> Actually, those programming languages that use delimiting characters
> for symbols often use different symbols for different categories of
> symbols.
the alphabet is exhausted already if you think this way -- there are lot 
of PV classes by now.

>  See, for example, this wikipedia page for some examples and
> historic perspective:
>
> http://en.wikipedia.org/wiki/Sigil_(computer_programming)
>
> Most of the pseudo variables, are, in fact, just hidden functions that
> perform complex magic to retrieve a piece of information from the SIP
> message, for example.
same is for avps - a hidden function accessing a linked list in shared 
memory. Moreover, ser mode of avps encodes the list in the name (in K 
there is only one avp list, while in S are couple of them). Further, 
$shv(xyz) is accessing a fixed location in shared memory, $var(abc) is 
accessing a fixed location is private memory, a.s.o. ... we can move all 
to $ or all to @.

Daniel

>  This is definitely true for selects in SER and
> it is, as far as I can tell, true for many of the PVs in Kamailio.
>
> When it comes to selects in SER, they are basically nothing more than
> just function names constructed in a special way. We use the '@'
> delimiter at the beginning of the function name to denote that this is
> a special kind of function which cannot be used like other function in
> the routing part of the script. There is no reason why selects should
> use the same delimiter that is used for variables (in case of SER AVPs
> because there are no real variables).
>
>   
>> Basically, there are classes of script variables, some accepting dynamic
>> names (like avps $avp(...), headers $hdr(...), private $var(...) and shared
>> variables $sht(...) a.s.o.).
>>
>> I do not see reason for a special character for certain classes, like avp or
>> select. It is much much clearer to have:
>> $avp(name)
>> $sel(name)
>>     
>
> Why is it clearer to overload one delimiter for different kinds of
> symbols than to use multiple delimiters? Under the hood, selects are
> something completely different than AVPs. Pseudo variables like $fd
> are something very different than $var(..), and so on.
>
> And if this is the preferred approach, wouldn't it make more sense to
> call functions as $func(name) as well? Just to be consistent?
>
>   
>> rather than:
>> $name for avps
>> @name for selects
>> &name, %name etc. for what so ever variable class
>>     
>
> This form is much more compact, easier to read, and also similar to
> how other programming languages treat different categories of symbols.
> Note that in your example above you do the same thing, only in a more
> complex way.
>
>    Jan.
>
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