deparse(substitute(x)) fails in implied call to an S3 print method

On 07/05/2017 3:56 PM, Spencer Graves wrote:

In an implied call to an S3 print method, deparse(substitute(x)) returns
"x", regardless of the name of object in .GlobalEnv, as indicated in the
following:

 > Xnamed <- 1
 > class(Xnamed) <- 'name.x'
 > print.name.x <- function(x, ...){

+   namex <- deparse(substitute(x))
+   cat('How can I get the name of x in .GlobalEnv?\n',
+       'deparse(substitute(x)) gives only ', namex, '\n')
+ }

 > Xnamed

How can I get the name of x in .GlobalEnv?
  deparse(substitute(x)) gives only  x


       My real application is print.findFn{sos}, which displays in a web
browser.  If the results of multiple searches are "printed", the name of
the object in .GlobalEnv could help the user keep track of what was 
done.

I don't think there's any way around this.  Auto-printing of Xnamed 
isn't equivalent to print(Xnamed); it doesn't happen until after 
Xnamed is evaluated.  It assigns the result to a local variable called 
x, and calls print(x).  (All of this is done in C code, and at that 
point I don't think the original expression "Xnamed" is available any 
more.)

For your application, you may have to allow users to attach names to 
the object.  I don't know how you're creating those things, but part 
of the work could save a name as an attribute "SOSname", and then the 
print method would use that.

Duncan Murdoch

       Thanks,
       Spencer Graves

 > sessionInfo()

R version 3.4.0 (2017-04-21)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Sierra 10.12.4

Matrix products: default
BLAS:
/System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib 

LAPACK:
/Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib 


locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods base

loaded via a namespace (and not attached):
[1] compiler_3.4.0 tools_3.4.0