Improve checking of parameter inputs to parameters() and grid_*() functions #422

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1. hfrick

   added

   upkeep

   on Feb 3, 2026
2. hfrick commented on Feb 24, 2026

   

   hfrick

   on Feb 24, 2026

   MemberAuthor

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   Looking at this from the perspective of the outcome, i.e., the error messages, rather than the code structure. Note that the nice-looking error message in validate_params() about which elements should be param objects never actually fires because it's caught in parameters() first.

   library(dials)
   #> Loading required package: scales
   
   # constructor -----------------------------
   
   # no input
   # should error (for now) but has a cli error that shouldn't show
   parameters() 
   #> Error:
   #> ! ! Could not evaluate cli `{}` expression: `x`.
   #> Caused by error in `eval(expr, envir = envir)`:
   #> ! argument "x" is missing, with no default
   
   # dispatch from param object
   ## should error but doesn't tell you which one is wrong
   parameters(mtry(), "min_n") 
   #> Error in `parameters()`:
   #> ! The objects should all be <param> objects.
   
   # dispatch from list
   ## should error but doesn't tell you which one is wrong
   parameters(list(mtry(), "min_n"))
   #> Error in `parameters()`:
   #> ! The objects should all be <param> objects.
   
   
   # grid functions ----------------------
   
   # should this error or just return an empty tibble? # #428
   # if it should error, it needs a better error message
   grid_regular() 
   #> Error in `UseMethod()`:
   #> ! no applicable method for 'grid_regular' applied to an object of class "NULL"
   
   # dispatch from param object
   ## fires from constructor, 
   ## thus doesn't tell you which one is wrong *and* 
   ## has the wrong call
   grid_regular(penalty(), "min_n")
   #> Error in `parameters()`:
   #> ! The objects should all be <param> objects.
   
   # dispatch from list
   ## fires from constructor, 
   ## thus doesn't tell you which one is wrong *and* 
   ## has the wrong call
   grid_regular(list(mtry(), "min_n"))
   #> Error in `parameters()`:
   #> ! The objects should all be <param> objects.

   ^{Created on 2026-02-23 with reprex v2.1.1}
3. hfrick

   changed the title [-]Consolidate `check_list_of_param()` and `validate_params()`[/-] [+]Improve checking of parameter inputs to `parameters()` and `grid_*()` functions[/+] on Apr 8, 2026
4. hfrick

   closed this as completedin #437on Apr 8, 2026