R devel - Oct 2018 - bug with OutDec option and deferred_string altrep object

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

	[[alternative HTML version deleted]]

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 at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu

This is now fixed in R-devel. Will port to R_patched in due course.
R_inspect also now handles pairlists ending with dotted pairs.

Best,

luke

On Tue, 9 Oct 2018, Tierney, Luke wrote:
> 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 at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu