[R] invisible() - does not return immediately as return() does

Christos Hatzis
Fri, 11 Aug 2006 20:59:29 -0000

Hi,

The difference is in the _return_ value of the function.

E.g.
> foo <- function() { cat("before\n"); cat("after\n");
return("done")}
> foo()
before
after
[1] "done"

i.e. returns the return value "done".

However
> foo2 <- function() { cat("before\n");
cat("after\n"); invisible("done")}
> foo2()
before
after

does not show the return value (invisible), but it actually returns it
invisibly:

> x <- foo2()
before
after
> x
[1] "done"


HTH.

-Christos

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Matthias Burger
Sent: Friday, August 11, 2006 4:45 PM
To: r-help at stat.math.ethz.ch
Subject: [R] invisible() - does not return immediately as return() does


Hi,

I stumbled across the following (unexpected for me) behavior after replacing
a return() statement in the middle of a function by invisible().

Example:
foo <- function() { cat("before\n"); return();
cat("after\n")}
>foo()
before
NULL

foo2 <- function() { cat("before\n"); invisible(TRUE);
cat("after\n")}
>foo2()
before
after

I expected invisible to have the same behavior as return, namely immediately
return execution to the calling environment.

I rechecked ?invisible and ?return
and here I read in section 'See Also'
[...]
'invisible' for 'return(.)'ing _invisibly_.

Do I just misunderstand what this implies?
Put another way what is the intention behind invisible() continuing until
the last statement before returning? ?invisible does not hint at this.


Regards,

  Matthias


>R.version.string
[1] "Version 2.3.1 (2006-06-01)"

same behavior in R 2.2.1 or
R.version.string
[1] "R version 2.4.0 Under development (unstable) (2006-07-29 r38715)"

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