| .Alias {base} | R Documentation |
.Alias creates an alias to another (part of) an R
object which is more (memory-) efficient than usual assignment.
new <- .Alias(expr)
expr |
an R expression; typically a name. |
new |
new name by which expr can be accessed. |
an identical copy of expr.
This has a dangerous semantic, and consequences can be
unexpected (it can be used to defeat the call-by-value illusion).
Know what you are doing before using .Alias!
<- for usual assignments.
mop <- options()
mop$browser <- "a browser" # not set on all platforms
Op <- .Alias(mop)
## A change to mop is reflected in Op and vice versa
## -- ONLY if no new slots are created ...
mop$digits <- "Wow!"
Op$browser <- "another one"
mop$browser; Op$digits
all(names(mop) == names(Op) &
sapply(seq(mop), function(i) all(Op[[i]] == mop[[i]])))
##> TRUE -- Op and mop ARE the same thing !
mop$newslot <- pi #--->> 'newslot' ==> (shallow) COPY of 'mop'
Op$newslot # R: still the old one, i.e. NULL
all(names(mop) == names(Op))# no longer TRUE