Write protecting objects

Is there a function to write protect a matrix  or list ?

I have considered making a duplicate copy. But I am wondering if
alternatives exist. Thanks.

You could do this up to a point by defining a class with nonfunctional
subscripting methods

data(trees)
class(trees)<-c("nowrite",class(trees))
"[<-.nowrite"<-function(x,...) {stop("Write protected")}
"[[<-.nowrite"<-function(x,...) {stop("Write protected")}
trees[3,4]<-4

Error in "[<-.nowrite"(*tmp*, 3, 4, value = 4) :
        Write protected

trees[3,]<-trees[2,]

Error in "[<-.nowrite"(*tmp*, 3, , value = trees[2, ]) :
        Write protected

but this can't protect you against

data(hills)
trees<-hills

and it doesn't even seem to work on $

"$<-.nowrite"<-function(x,...) {stop("Write protected")}
trees$Girth<-trees$Volume

You probably want a duplicate copy.

	-thomas



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