On 13/11/2009 6:39 PM, Gabor Grothendieck wrote:
Note that one should use inherits = FALSE argument on get and exists
to avoid returning objects from the parent, the parent of the parent,
etc.
I disagree. Normally you would want to receive those objects. If you
didn't, why didn't you set the parent of the environment to emptyenv()
when you created it?
Duncan Murdoch
On Fri, Nov 13, 2009 at 2:27 PM, Duncan Murdoch <murd...@stats.uwo.ca> wrote:
On 11/13/2009 2:03 PM, Trishank Karthik Kuppusamy wrote:
Greetings everyone,
I have a question about the default behaviour of a missing entry in an
environment.
Let us look at the following sequence of R statements:
e <- new.env()
e$a <- 1
e$a
[1] 1
e$b
NULL
I think I understand the logic for returning NULL to a missing entry in an
environment,
but I do not think that it is fully justified.
I am sure that the R developers must have seen this argument before,
but I wish to call for attention to this problem again,
because I think that it is important to the default safety of the R
programming language.
You get the same behaviour when asking for a nonexistent element of a list,
or a nonexistent attribute. If you want stricter checking, don't use $,
use get():
get("b", e)
Error in get("b", e) : object 'b' not found
or check first with exists():
exists("b", e)
[1] FALSE
I suppose that one could argue that a good R programmer must be careful
not to use NULL in any of his environment entries,
but I think it is better to remove altogether this burden from the
programmer
and simply raise a good, old-fashioned exception when the "$" operator
encounters a missing entry in an environment.
But then it would be inconsistent with what it does in other situations.
Duncan Murdoch
The biggest advantage is that it will easily eliminate a whole class of
programming error.
The biggest disadvantage is that it is not backwards-compatible with old R
programs.
I suppose a personal solution would be to simply redefine the "$" operator
in my programs.
However, I really do think that the default safety of an R environment
matters very much.
At the very least, it would be nice to be able to configure the safety of
a new environment,
perhaps through a parameter.
-Trishank
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