R/copy.R

In decisionpatterns/r-hash: A Hash/Dictionary/Map/Associated Array for R

#' copy 
#' 
#' Create a *copy* of a hash. 
#'
#' @param x hash
#' @param ... additional arguments
#'       
#' Creatinga copy using the assingment operator, `<-`, does not work as 
#' expected, since hashes are based on environments and environments are 
#' reference objects in R.  The assignment operator consequently creates a 
#' linked copy the original hash and not an independent copy.  The `copy` 
#' method provides an identical unlinked copy of the hash.
#' 
#' @return hash, copy of hash `x`
#' 
#' @author Christopher Brown
#' 
#' @seealso 
#'   [base::environment()]
#' 
#' @examples
#'   h <- hash( a=1, b=2 )
#'   g <- h
#'   g$a <- "foo"
#'   h$a     # "foo" 
#'   
#'   h_new <- copy( h )
#'   h_new$a <- "bar"
#'   h$a     # still "foo"
#'   
#' @name copy
#' @rdname copy
#' @docType methods
#' @export

setGeneric( 'copy', function(x,...) standardGeneric( 'copy'  ) )


#' @name copy,hash-method
#' @rdname copy

setMethod( 'copy', 'hash', 
  function(x, ... ) { 
    len <- length(x)
    if( len == 0 ) {
      hash()
    } else {
      hash( mget( keys(x), x@.Data ) ) 
    }
  }
)