[QGIS-Developer] $scale vs @map_scale - QGIS v2 vs v3

[Nyall Dawson]

On Mon, 21 Jan 2019 at 22:52, Andreas Neumann <a.neumann at carto.net> wrote:
>
> Hi,
>
> When migrating our version 2 to version 3 projects, most of our symbology needs revision, because our data-defined properties used a lot the "$scale" variable.
>
> What is the exact reason that $scale fails in version 3 and had been replaced by @map_scale?
>
> Is there really no upgrade path for this? We have many, many projects, and almost all of them need to be upgraded in version 3 to use "@map_scale" instead of "$scale".

There is a technical reason behind this, but there's also no technical
reason we couldn't make $scale silently "alias" to @map_scale. My
original thinking was that I wanted to strip out some of these older
expression formats, and 3.0 was a good opportunity to do this. But I'm
happy to reverse this decision.

PR incoming.

Nyall