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

[Spencer Graves]

On 2017-05-07 3:46 PM, Duncan Murdoch wrote:
> 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.


       Thanks for the reply.  I'm already saving match.call() and 
displaying that.  That's adequate, but I was hoping to do better.


        Spencer Graves

>
> 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
>>
>> ______________________________________________
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>>
>