## Example of String class using S3 methods.
## similar to String class in ruby.
## some functions from xtable code

## make a String object
string <- function(x) {
  if (!is.String(x)) {
    x = as.character(x)
    class(x) <- "String"
  }
  return(x)
}

## test if a String object
is.String <- function(x) return(class(x) == "String")


## give some basic definitions: length, summary, show, print
## give the length
length.String <- function(x,...) return(nchar(x))
summary.String <- function(x,...) return(table(strsplit(x,"")))
print.String <-function(x,...) cat(x,"\n") 

## some methods for access the String
slice = function(x,index) UseMethod("slice")
slice.String <- function(x,index) {
  tmp = unlist(strsplit(x,""))[index]
  return(string(paste(tmp,sep="",collapse="")))
}

## Concatanation
concat = function(x,y,sep="") UseMethod("concat")
concat.String = function(x,y,sep="") {
  x <- string(paste(x,string(y),sep=sep))
  return(x)
}
## repeat a String
rept.String = function(x,n) string(paste(rep(x,n),sep="",collapse=""))

## split a String. Return a vector of character type. Can't
## return a vector of "String" type, only a list.
split.String <- function(x,y="") unlist(strsplit(x,y))

## upcase/downcase
upcase = function(x) UseMethod("upcase")
upcase.String <- function(x) toupper(x)
downcase = function(x) UseMethod("downcase")
downcase.String <- function(x) tolower(x)

## syntactical shortcuts
"[.String" <- function(x,index) slice(x,index)
"+.String" <- function(x,y) concat.String(x,y)
"*.String" <- function(x,y) rep.String(x,y)
"/.String" <- function(x,y) split.String(x,y)