[QGIS-Developer] Typed Variables?

[Andreas Neumann]

Hi Nyall, 

Thank you very much for your detailed reply. Good to hear that there is
an interest in making this happen. Is this something that could be added
during QGIS 3.x life span or would this have to wait for QGIS 4.x? Would
this be something for a 2021 QGIS grant? 

About my specific scenario: 

I was looking for a to_boolean() conversion function - but it doesn't
exist. Would the alternative "eval(@debugging)" be the way here - are
there any downsides of using eval() in this context? @debugging would
hold a string 'true' or 'false'. 

Greetings, 

Andreas 

On 2020-06-12 02:15, Nyall Dawson wrote:

> On Thu, 11 Jun 2020 at 01:26, Andreas Neumann <a.neumann at carto.net> wrote: 
> 
>> Hi,
>> 
>> I have a question about the variables that can be defined on different scopes. They are most of the times (or always?) strings, if I manually define them - right?
> 
> If you manually define them, then yes -- they are always strings.
> 
>> Some of the automatic variables might be of a different type (like date, layer, etc.)
> 
> Correct. The underlying API allows for any variant type value (just
> like expressions), so potentially a variable could be a int, date,
> datetime, string, list, map, interval, feature, etc...
> 
>> Can I also manually define a "typed" variable? E.g. a boolean true instead of 'true' as a string?
> 
> Only via PyQGIS, not via the UI.
> 
> It's been requested in the past that we support expose an option for
> these. And I'd like to see this happen, because then we could improve
> the UI for entering variable values in the variable list widget. E.g.
> if a variable has been defined on a project level as a "color" type
> variable, it would be nice to make it so that when you override this
> variable for a particular layout item you get a color picker widget.
> And similarly, if you defined a variable to be of the type "font
> name", then the tree widget could show a drop down list of available
> fonts. It would certainly help make them more accessible.
> 
> It's actually somewhat of a dream of mine to expose variable editing
> better in the QGIS UI to users. E.g. - via variables its completely
> possible to make symbols which alter their appearance. So already have
> this concept of "smart symbols", where you could have a marshland
> symbol which alters its appearance based on variables like
> "@height_of_vegetation" and "@density_of_vegetation" and
> "@health_of_vegetation". That's possible today. But to modify these
> variables you need to go into the raw variable editor for the layer
> and tweak their. What would be great is if we did things like expose
> them at the symbol selector dialog -- so that if a user picks your
> "marshland" smart symbol from the library, they don't see all the
> underlying symbol layers and those settings, but instead just see
> widgets for tweaking these specific @height_of_vegetation/...
> variables.  This is where "typed" variables would be a necessity!
> 
> Nyall
> 
>> That way I could directly use variables without having to add CASE WHEN END statements ...
>> 
>> My use case would be to have a boolean "debugging" variable. If it is set to true, then certain parts of the form with internal IDs would be visible, if set to false, they would be hidden.
>> 
>> Thanks,
>> 
>> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20200612/647cd6dd/attachment.html>