Re: [R] Does R have a "const object"?

From: Duncan Murdoch <murdoch.duncan_at_gmail.com>
Date: Tue, 15 Mar 2011 16:46:57 -0400

On 15/03/2011 2:35 PM, Martin Morgan wrote:
> On 03/15/2011 11:34 AM, Duncan Murdoch wrote:
> > On 15/03/2011 2:23 PM, Uwe Ligges wrote:
> >>
> >> On 15.03.2011 15:53, xiagao1982 wrote:
> >> > Hi, all,
> >> >
> >> > Does R have a "const object" concept like which is in C++ language?

> >> I want to set some data frames as constant to avoid being modified
> >> unintentionally. Thanks!
> >>
> >>
> >> Although there is almost never a "No" in R, the best short answer is:
> >> "No".
> >
> > Very nice answer! Achim, this is a fortune candidate if I ever saw one!
>
> but aren't lockBinding / lockEnvironment a reasonable longer answer? Martin

I think the limitations would also need to be part of the long answer, and probably a discussion of environments and scoping rules. For example,

x <- 1
lockBinding("x", environment())
f <- function() {

   print(x) # I can see and print the locked variable    x <- 2 # And change it? (Not really....)    print(x)
}
f() # prints a 1 then a 2

Duncan Murdoch



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