Warning if an object from an old mlr3-version is loaded

[mb706]

Loading e.g. a Task that was generated with an old mlr3-version using readRDS() will give errors like this: https://github.com/mb706/autoxgboost3/issues/2#issuecomment-596969950 . Maybe there is a way to make these kinds of errors more obvious to the user.

[pat-s]

Is this related to the change of the serialization version in saveRDS() in >= R 3.6.0?

[mb706]

no, this is just from changing the API of R6-objects. In S3 this is less of an issue; if the data layout does not change then "old" objects can be used with new versions of a software. With R6 the objects themselves carry their functions with them and are more likely to be incompatible with updates.

[mllg]

I wonder if it would be best to have a special serialize/deserialize method for the objects. This way we would only save the data and would be able to fix API changes during deserialization/reconstruction.

[mb706]

it would be nicer to work with R's own serialization because that also works when the task is "hidden" somewhere in a list or environment of a function (e.g. objective function of an optimization algorithm). I can see though that this is technically difficult to implement.

[thesnowkeepsfalling]

Hi - not sure if this belongs here, but I found an example which may be a clash from another package.

> library("mlr3")
> 
> #load an example
> task = tsk("pima")
> print(task)
<TaskClassif:pima> (768 x 9)
* Target: diabetes
* Properties: twoclass
* Features (8):
  - dbl (8): age, glucose, insulin, mass, pedigree, pregnant, pressure, triceps
> 
> learner = lrn("classif.rpart")
> learner$param_set
ParamSet: 
               id    class lower upper levels     default value
1:       minsplit ParamInt     1   Inf                 20      
2:      minbucket ParamInt     1   Inf        <NoDefault>      
3:             cp ParamDbl     0     1               0.01      
4:     maxcompete ParamInt     0   Inf                  4      
5:   maxsurrogate ParamInt     0   Inf                  5      
6:       maxdepth ParamInt     1    30                 30      
7:   usesurrogate ParamInt     0     2                  2      
8: surrogatestyle ParamInt     0     1                  0      
9:           xval ParamInt     0   Inf                 10     0
> 
> #load example param set
> library("paradox")
> tune_ps = ParamSet$new(list(
+   ParamDbl$new("cp", lower = 0.001, upper = 0.1),
+   ParamInt$new("minsplit", lower = 1, upper = 10)
+ ))
> 
> #we can see the contents: 
> tune_ps
ParamSet: 
         id    class lower upper levels     default value
1:       cp ParamDbl 0.001   0.1        <NoDefault>      
2: minsplit ParamInt 1.000  10.0        <NoDefault>      
> 
> #but when we load another package 
> library(ParamHelpers)
> tune_ps #we cannot see the contents: 
[1] "Empty parameter set."

[mb706]

FYI this is known internally, but idk if / where we have the issue about this. It's just broken, don't load old and new mlr (or paradox & ParamHelpers) in the same R sessionl. Sorry about this :-(

[berndbischl]

we agrreed that we woukd store the version nr of the parent package, by doing this in leanify.

in general, this a complicated topic. we could later either

• separate logic / class code better from the data
• maybe ship converter function for old mlr object versions