How to dynamically creat blank GRanges?

I want to create a blank GRanges (from package GenomicRanges) object dynamicall.

If we have two alternative options, opt1 and opt2, we can write statically as:

library(GenomicRanges)
GRanges(seqnames=NULL,ranges=NULL,strand=NULL, opt1=NULL, opt2=NULL)

The question is "How can we create the GRanges object dynamically?". Or more specifically, "Is the following functionXX possible?" :

opts=c('opt1','opt2','opt3')
#' dynamic create blank GRanges with optional fields
#' @param opts, a vector containing the colnames of "mcols" of GRanges object
#' @return  blank GRanges object
functionXX<-function(opts){
   //todo:
}

Thanks!

Only the column names is not enough, every fields should have the defined data types.

Below is the solution:

opts=c('opt1','opt2','opt3')   
tp=list(character(),character(),character())   
functionXXX<-function(opts,tp){
    names(tp)=opts
    df=do.call(data.frame,tp)
    gr=GRanges(c(seqnames=NULL,ranges=NULL,strand=NULL)) 
    mcols(gr)=df
    gr
  }
functionXXX(opts,tp)
#GRanges object with 0 ranges and 3 metadata columns:
# seqnames    ranges strand |        opt1        opt2        opt3
#  <Rle> <IRanges>  <Rle> | <character> <character> <character>
#-------
#seqinfo: no sequences