r - Using "[[ ]]" notation for reference class methods -

while experimenting new reference classes in r noticed odd behaviour if use "[[ ]]" notation methods (x[["dosomething"]] instead of x$dosomething). notation works fields, thought wouldn't work methods until found if execute "class(x$dosomething)" can use "[[ ]]" afterwards. simple example below illustrates point.

setrefclass("number",    fields = list(     value = "numeric"   ),   methods = list(     addone = function() {       value <<- value + 1     }   ) )  x <- new("number", value = 1)  x[['value']]         # 1  x[["addone"]]()      # error: attempt apply non-function class(x[["addone"]]) # null  class(x$addone)      # "refmethoddef"  # following works! x[["addone"]]()      # sets x$value = 2 class(x[["addone"]]) # "refmethoddef" 

the reason encountered because want group objects in list , create "applymethod" function applies specified method on each of objects within. therefore, need specify method string. have ideas how can achieve this?

here's class

.a <-     setrefclass("a",                 fields=list(x="numeric"),                 methods=list(foo=function() x)) 

if had instance a , wanted construct call 'foo' method using '$' could

eval(substitute(a$fun(), list(fun="foo"))) 

so i'll create class alist meant have list of elements of class a (this enforced programmatically), , has .delegate method that'll apply arbitrary method elements of list. i'll add method delegates foo.

.delegate <- function(fun, ...) {     lapply(elts, function(elt, ...) {         eval(substitute(elt$fun(...), list(fun=fun, ...)))     }) }  .alist <-     setrefclass("alist",                 fields=list(elts="list"),                 methods=list(                   initialize = function(...) callsuper(elts=list(...)),                   .delegate = .delegate,                   foo=function() .delegate("foo"))) 

and use it

> alist <- .alist$new(.a$new(x=1), .a$new(x=2)) > alist$foo() [[1]] [1] 1  [[2]] [1] 2