[SR-Dev] operators and variables

Andrei Pelinescu-Onciul andrei at iptel.org
Thu Dec 11 22:01:40 CET 2008

It would be better to have different operators for strings and for
integers. Right now we have '+', '==' and '!=' that can be used both for
strings and integers. The problem with this approach is that it makes
some optimizations impossible, especially when combined with dynamic
typed variables (avps or pvars). '+' is especially bad because one
can tell what type ($v + x) has only at runtime.

I think having perl like operators would help a lot:

- '.' for string concatenation (instead of reusing '+'), e.g.: 
 $v= "foo" .  "bar"
- 'eq' instead of == for strings, e.g.: $v eq "bar" 
- 'ne' instead of != for strings, e.g.: $v ne "bar"

We could support them right now in parallel with the old ones and 
 obsolete +, ==  and != for strings in the future (but that means we
 still cannot optimize '+' in all the cases) or switch right now
(maybe with some old compat switch which will support old scripts
The question is how much are they used right now. While I think '==' and
'!=' are used quite often, I'm not sure about '+' for strings (and '+'
is the most important anyway).
Note: we can still support '==' and '!='  for condition tests not
involving variables (e.g. method=="INVITE", uri=="sip:foo" a.s.o.).

Another advantage that this change would bring is better type checking
 at startup (more errors flagged without having to run the script) and
 possible implicit conversions (e.g. int to string or string to int) if
 we decide to support them.

Any comments?

In the future it would also be much better to have typed script vars
(e.g. int $var1). This would help a lot in checking the script for
correctness. With the dynamic typed vars, one has to run the script to
find errors. It would also help in optimizing, but not so much if we
 separate the operators, like above.


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