This PR follows up on#4271 and#5444, aiming tofix#4269.

Like before, it aims to provide the convenience of setting some scale parameters, without comitting to a full scale yet.
Unlike#5444, this PR is closer to Claus' approach in#4271.

This PR thescale_params() function that populates a newScalesList$params field. When a new scale is added, it will get updated with the parameters in that field. The update mechanism required the most attention. Every<Scale> class now has aScale$new() method that takes on most of the work thatcontinuous_scale(),discrete_scale(),binned_scale() constructors were doing before. TheScale$update() method is a thin wrapper around this and should resolve gnarly situations (e.g. limit transformation).

In the demo below we can note:

• the y-limits are appropriately transformed by the sqrt transformation. If we were to use the transform first and then the limits, the result would be the same.
• We can set parameters for multiple scales at once, like colour/shape.

devtools::load_all("~/packages/ggplot2/")#> ℹ Loading ggplot2p<- ggplot(mpg, aes(displ,hwy,colour=drv,shape=factor(year)))+  geom_point()p+  scale_params("x",breaks= c(2,4,7))+  scale_params("y",limits= c(0,50))+  scale_params("y",transform="sqrt")+  scale_params(c("colour","shape"),guide= guide_legend(ncol=2))

The update mechanism should also recognise invalid updates:

p+ scale_params("colour",foobar="i dont exist")#> Error in `geom_point()`:#> ! Problem while computing aesthetics.#> ℹ Error occurred in the 1st layer.#> Caused by error in `scale_colour_discrete()`:#> ! Cannot update scale with the unknown argument:#> • "foobar"

^{Created on 2024-11-22 withreprex v2.1.1}