r - Inheritance leads to error when using reference class -

here code:

myclass = setrefclass("myclass",                        fields = list(                            fa = "numeric",                            fb = "numeric",                            filename = "character",                            data = "data.frame"                        ) )   myclass$methods(     initialize = function(fa = 0, fb = 0, filename = "") {         message("initializing object in class...")         .self$fa = fa         .self$fb = fb         .self$data = read.table(.self$filename, header=true)     } )   # myclass1 = setrefclass("myclass1", #                        fields = list( #                            fc = "numeric" #                        ), #                        contains = "myclass" # ) #  # myclass1$methods( #     initialize = function(..., fc = 0) { #         message("initializing object in class1...") #         callsuper(...) #         .self$fc = fc #     } # ) #  # myclass2 = setrefclass("myclass3", #                        fields = list( #                            fd = "numeric" #                        ), #                        contains = "myclass1" # ) #  # myclass2$methods( #     initialize = function(..., fe = 0) { #         message("initializing object in class2...") #         callsuper(...) #         .self$fe = fe #     } # ) 

this loads ok. if uncomment subclasses r complain when loading:

==> r cmd install --no-multiarch --with-keep.source testloadref  * installing library ‘/library/frameworks/r.framework/versions/3.1/resources/library’ * installing *source* package ‘testloadref’ ... ** r ** preparing package lazy loading initializing object in class... error in file(file, "rt") : invalid 'description' argument error : unable load r code in package ‘testloadref’ error: lazy loading failed package ‘testloadref’ * removing ‘/library/frameworks/r.framework/versions/3.1/resources/library/testloadref’ * restoring previous ‘/library/frameworks/r.framework/versions/3.1/resources/library/testloadref’  exited status 1. 

i not know why, parent's class initialize method called setrefclass. therefore should ensure parent class can constructed no arguments. e.g.:

myclass$methods(   initialize = function(fa = 0, fb = 0, filename = "") {     message("initializing object in class...")     .self$fa = fa     .self$fb = fb     if (nzchar(filename)) {       .self$data = read.table(.self$filename, header = true)     }   } )