[QGIS-Developer] Variable syntax: $ vs @

[Stefan Keller]

Thanks Nathan for merging [1].
Now looking forward to the new release of the Expressions Plus QGIS plugin :-).

:Stefan

[1] https://github.com/NathanW2/qgsexpressionsplus/pull/8#issuecomment-312486509


2017-06-30 12:21 GMT+02:00 Stefan Keller <sfkeller at gmail.com>:
> Hi Nathan
>
> Only partially related to this thread as a shy reminder:
> My intern Simran recently has made a pull request [*] for your nice
> Expressions Plus Plugin QGIS plugin.
>
> These are the proposed additional functions:
> * max_incremented() - an "autoincrement" id function
> * hstore - support of a key-value pair set/string
> * nullif() - returns None if arg_1 equals to arg_2 otherwise arg_1
> * get_env_variable() and set_env_variable()
> * jitter_geometry()
>
> These expression functions could be of interest for workshops like the
> mentioned one.
>
> Cheers, Stefan
>
> [*] https://github.com/NathanW2/qgsexpressionsplus/pull/8
>
>
> 2017-06-19 14:36 GMT+02:00 Neumann, Andreas <a.neumann at carto.net>:
>> Hi Nathan,
>>
>> Thank you for the explanation. Makes sense. I will pass this on in the
>> workshop.
>>
>> Andreas
>>
>> On 2017-06-19 14:12, Nathan Woodrow wrote:
>>
>> Hey Andreas,
>>
>> They are really two different things.  $geometry is really a function that
>> takes no arguments. This has been deprecated in favour calling with () e.g
>> geometry().  @ is only for variables.
>>
>> So you can explain it that $ used to be a shorthand way of calling a
>> function that took no arguments which has now been replaced with () at the
>> end to call it. $area = area().  This becomes important because now we
>> support optional arguments meaning you can take 0 to N arguments.
>>
>> - Nathan
>>
>> On Mon, Jun 19, 2017 at 9:53 PM, Neumann, Andreas <a.neumann at carto.net>
>> wrote:
>>>
>>> Hi,
>>>
>>> While preparing for a workshop on expressions I wonder how to explain why
>>> some variables are referenced with the $ sign (like $geometry) while other
>>> variables start with the @ sign, like @row_number, @layer_name.
>>>
>>> I know that it has historical reasons and that variables with the @ sign
>>> are newer and are implemented using a different technology.
>>>
>>> But are there plans to get rid of the old $ sign notation and move
>>> everything to the @ sign notation?
>>>
>>> Just wonder how I best explain this to the participants of the workshop.
>>>
>>> Thanks for your reply,
>>>
>>> Andreas
>>>
>>>
>>>
>>> _______________________________________________
>>> QGIS-Developer mailing list
>>> QGIS-Developer at lists.osgeo.org
>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>>
>>
>>
>>
>>
>> _______________________________________________
>> QGIS-Developer mailing list
>> QGIS-Developer at lists.osgeo.org
>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer