[Rd] bug with OutDec option and deferred_string altrep object

[Tierney, Luke]

Thanks for the report. The approach you outlines below should work --
I'll look into it.

Best,

luke

On Mon, 8 Oct 2018, Michael Sannella wrote:

> While implementing R's new 'altrep' functionality in the TERR engine,
> I discovered a bug in R's 'deferred_string' altrep object: it is not
> using the correct value of the 'OutDec' option when it expands a
> deferred_string.  See the following example:
> 
> R 3.5.1: (same results in R 3.6.0 devel engine built 10/5)
>     > options(scipen=0, OutDec=".")
>     > as.character(123.456)
>     [1] "123.456"
>     > options(scipen=-5, OutDec=",")
>     > as.character(123.456)
>     [1] "1,23456e+02"
>     > xx <- as.character(123.456)
>     > options(scipen=0, OutDec=".")
>     > xx
>     [1] "1.23456e+02"
>     >
> 
> In the example above, the variable 'xx' is set to a deferred_string
> while OutDec is ','.  However, when the string is actually formatted
> (when xx is printed), it uses the current option value OutDec='.' to
> format the string.  I think that deferred_string should use the value
> OutDec=',' from when as.character was called.
> 
> Note that the behavior is different with the 'scipen' option: The
> deferred_string object records the scipen=-5 value when as.character
> is called, and uses this value when xx is printed.  Looking at the
> deferred_string object, it appears that CDR(R_altrep_data1(<obj>)) is
> set to a scalar integer containing the scipen value at the time the
> deferred_string was created.
> 
> Ideally, the deferred_string object would save both the scipen and
> OutDec option values.  I'd suggest saving these values as regular
> pairlist values, say by setting the data1 field to pairlist(<source>,
> scipen=-5L, OutDec=',') for the value of xx above.  To save space, you
> could avoid saving these values in the common case where scipen=0L,
> OutDec='.'.  It would also be better if the data1 field was a
> well-formed pairlist; the current value of the data1 field causes
> R_inspect to segfault.
> 
> I understand that you probably wouldn't want to change the
> deferred_string structure.  An alternative fix would be to avoid this
> case by:
>   1. Never create a deferred_string if OutDec is not '.'.
>   2. When expanding an element of a deferred_string, temporarily set
> OutDec to '.'.
> 
>   ~~ Michael Sannella
> 
> 
>

-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu