R help - Aug 2006 - 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)"

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)"

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Matthias Burger <matt.burger at web.de> writes:
> 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.
I can understand the confusion, but I think invisible is intended to
return its argument "invisibly" and actually has nothing to do with
returning from a function (except that is where you are going to use
it almost always ;-).  

So you want return(invisible(foo)) in the middle of a function.


The man page for invisible says:
  
   Return a (temporarily) invisible copy of an object.

But the man page for return has the return(.)'ing _invisibly_
statement which I think is confusing.

Cheers,

+ seth