Getting rid of S4 classes

[stefvanbuuren]

Somewhere is mice I stated that

#' @note The \code{mice} package does not use 
#' the S4 class definitions, and instead relies on the S3 list 
#' equivalent \code{oldClass(obj) <- "mids"}.

There are - however - S4 setClass() definitions for mads and mira. I believe that these functions do not use any of the additional functionality offered by S4. If true, it would be preferable to turn these into S3-classes.

[stefvanbuuren]

I tried to remove setClass() and make the definition of mads and mira similar to mids and mipo. However, for some unclear reason, this yields "export errors" from R CHECK. I reverted to the old code, so this remain on the wish list for now.