[R] Dynamic Dictionary Data Type?

[Gabor Grothendieck]

On 6/2/05, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
> On Thu, 2 Jun 2005, hadley wickham wrote:
> 
> >> An environment is a hash table, and copying occurs only on modification,
> >> when any language would have to copy in this context.
> 
> Caveat: the default is new.env(hash=FALSE), so an environment is a hash
> table in one sense but not necessarily so in the strict sense.

Can you expand on this?  When would one use hash = TRUE vs.
the default?