R help - Jun 2007 - Determining whether a function's return value is assigned

Dear all,

Does R offer a means by which a function can determine
whether its return value is assigned? I am using R
2.4.1 for Windows.

Suppose what I am looking for is called
"return.value.assigned". Then one might use it like
this

    myfunction <- function () {
        # Create bigobject here

        if (return.value.assigned()) {
            bigobject
        } else {
            summary(bigobject)
        }
    }

and

    x <- myfunction()  # bigobject is assigned

    myfunction()       # summary of bigobject is printed

Octave and MATLAB have the nargout function that does
what I want, and Perl has the wantarray function
detecting the context in which a function is called.
Perhaps match.call() can be made to do what I want,
but, if so, I don't see it in reading the
documentation.

Sincerely,

Paul Laub

Paul Laub wrote:
> Dear all,
> 
> Does R offer a means by which a function can determine
> whether its return value is assigned? I am using R
> 2.4.1 for Windows.
Short answer: No.
Long answer: You want to have a class for the object called
"bigobject"
below and a print/show method that provides the summary for objects of 
that class.

Uwe Ligges




> 
> Suppose what I am looking for is called
> "return.value.assigned". Then one might use it like
> this
> 
>     myfunction <- function () {
>         # Create bigobject here
> 
>         if (return.value.assigned()) {
>             bigobject
>         } else {
>             summary(bigobject)
>         }
>     }
> 
> and
> 
>     x <- myfunction()  # bigobject is assigned
> 
>     myfunction()       # summary of bigobject is printed
> 
> Octave and MATLAB have the nargout function that does
> what I want, and Perl has the wantarray function
> detecting the context in which a function is called.
> Perhaps match.call() can be made to do what I want,
> but, if so, I don't see it in reading the
> documentation.
> 
> Sincerely,
> 
> Paul Laub
> 
> ______________________________________________
> 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.

On Sat, 30 Jun 2007, Paul Laub wrote:
> Dear all,
>
> Does R offer a means by which a function can determine
> whether its return value is assigned? I am using R
> 2.4.1 for Windows.
No
> Suppose what I am looking for is called
> "return.value.assigned". Then one might use it like
> this
>
>    myfunction <- function () {
>        # Create bigobject here
>
>        if (return.value.assigned()) {
>            bigobject
>        } else {
>            summary(bigobject)
>        }
>    }
That's what the print() function is for. Write a print() method.

 	-thomas