R: How come that "is" is TRUE, but "as" is impossible? -

the class "ecdf" inherits class "stepfun". if f such empirical cumulative density function, both is.stepfun(f) , is(f,"stepfun") true, , as.stepfun(f) doesn't expected. conversion of f "stepfun" as(f,"stepfun") impossible because of "metadata", if strict false:

f <- ecdf(1:10)  class(f) # [1] "ecdf"     "stepfun"  "function"  is.stepfun(f) # [1] true  is(f,"stepfun") # [1] true  identical(f,as.stepfun(f)) # [1] true  g <- as(f,"stepfun",strict=false) # error in as(f, "stepfun", strict = false) :  #   internal problem in as(): “ecdf” is(object, "stepfun") true, metadata asserts 'is' relation false 

so how is related as , meaning of "metadata" here?

i may have found relevant information. @ this nabble archive

but has 2 problems:   1) as() s4 method not work  (problem 2 not relevant) 

locally :-) this question has warnings trying use as()

so suggestion stick as.stepfun(foo) .