[Qgis-developer] Expression engine functions and naming

[Nyall Dawson]

Hi all,

I thought I'd raise an issue which has been on my mind a bit lately,
and I'm not sure how to proceed with fixing it. At the moment there's
a huge lack of consistency in function names in the QGIS expression
engine. Here's some examples:

- Some functions use the naming convention of seperating lowercase
words with underscores, for example "format_number", "format_date",
"color_rgb"
- Others use all lowercase, no underscore, eg "tostring", "wordwrap"
- Still others use camel case, eg "geomFromWKT", "symDifference"

Basically, we've got a mix of every naming convention possible. I
think there's an urgent need for us to choose a convention and ensure
that all newly introduced functions adhere to this.

The follow up question is whether or not we can clean up this mess.
Can we rename functions in a way that doesn't negatively impact users?
Possibly we could have aliases for functions which evaluate ok so that
older projects can still work, but which aren't shown the the user in
the dialog.

There's also some function names & formats which really bug me, specifically:
- "$feature", "$numfeatures". Ideally these should be named something
more appropriate like "$atlas_feature_num" and "$atlas_feature_count",
since they directly relate to atlas variables. From their names it
seems more logical that these would return the current feature and
number of features in the current layer.
- I made a dumb decision when I created the "clamp" function and put
the parameters in the "minimum,input,maximum" order. In retrospect
these should be "input,minimum,maximum"

I'm guessing there's nothing we can do to retrospectively fix these
inconsistencies now?

Cheers,
Nyall