[Rcpp-devel] strange bool conversion?

[Daniel Sabanés Bové]

Hi Dirk,

thanks for your quick response.

I think this is a bug if you as a programmer think "OK, Rcpp does nice
implicit conversion for me" and indeed it does not do the right thing.

Also note that this behaviour was only introduced in the previous
version of Rcpp, before my code worked without the explicit statement.
So previously working code was broken.

If you really decide to leave it as it is, I think you should at least
explicitly warn the user in the manuals.

Kind regards,
Daniel

-------- Original Message --------
Subject: Re: [Rcpp-devel] strange bool conversion?
From: Dirk Eddelbuettel <edd at debian.org>
To: Daniel Sabanés Bové <daniel.sabanesbove at ifspm.uzh.ch>
Date: Mon 10 Jan 2011 13:26:05 CET

> 
> On 10 January 2011 at 12:06, Daniel Sabanés Bové wrote:
> | Hi,
> | 
> | I have to report another serious bug in argument extraction, now with
> | integers.
> | (It seems to me that the fix by Romain could have been causing this
> | behaviour?)
> | Moreover, the problem does not depend on a "const" modifier:
> | 
> | -- snip --
> | 
> | library(Rcpp)
> | library(inline)
> | 
> | ## this compiles and loads fine, but is wrong:
> | wrong <- cxxfunction(signature(x="list") , '
> |          List input(x);
> |          int a = input[0];
> |          return wrap(a);
> |          ' , plugin = "Rcpp")
> | 
> | ## still OK:
> | wrong(list(1))
> | 
> | ## all 1:
> | wrong(list(4))
> | wrong(list(4L))
> | wrong(list(-4L))
> | 
> | 
> | ## this is correct:
> | correct <- cxxfunction(signature(x="list") , '
> |          List input(x);
> |          int a = as<int>(input[0]);
> |          return wrap(a);
> |          ' , plugin = "Rcpp")
> | 
> | correct(list(1))
> | wrong(list(4))
> | wrong(list(4L))
> | wrong(list(-4L))
> | 
> | -- snap --
> 
> So where is the bug?  
> 
> R> correct(list(a=42))
> [1] 42
> R> correct(list(a=42L))
> [1] 42
> R> correct(list(a=-42L))
> [1] -42
> R>  
> 
> There is nothing wrong with helping the compiler via explicit template use as
> in 
> 
> 	int a = as<int>(input[0]);
> 
> Dirk
> 
>  
> | The sessionInfo():
> | 
> | 
> | R version 2.12.1 (2010-12-16)
> | Platform: i686-pc-linux-gnu (32-bit)
> | 
> | locale:
> |  [1] LC_CTYPE=de_CH.utf8       LC_NUMERIC=C            
> |  [3] LC_TIME=de_CH.utf8        LC_COLLATE=de_CH.utf8   
> |  [5] LC_MONETARY=C             LC_MESSAGES=de_CH.utf8  
> |  [7] LC_PAPER=de_CH.utf8       LC_NAME=C               
> |  [9] LC_ADDRESS=C              LC_TELEPHONE=C          
> | [11] LC_MEASUREMENT=de_CH.utf8 LC_IDENTIFICATION=C     
> | 
> | attached base packages:
> | [1] stats     graphics  grDevices utils     datasets  methods   base    
> | 
> | other attached packages:
> | [1] inline_0.3.8 Rcpp_0.9.0 
> | 
> | loaded via a namespace (and not attached):
> | [1] tools_2.12.1
> | 
> | 
> | Kind regards,
> | Daniel
> | 
> | > This is fixed now (rev 2789). For the curious, it seems that the
> | > generic_proxy template made the wrong choice between these conversion
> | > operators: operator SEXP() const { return get() ; } template <typename
> | > U> operator U() const { return ::Rcpp::as<U>(get()) ; } I resolved
> | > this by forcing the conversion to bool with this: operator bool()
> | > const { return ::Rcpp::as<bool>(get()) ; } Thanks again for the
> | > report. Romain Le 13/12/10 17:30, Daniel Saban?s Bov? a ?crit :
> | >> > Hi,
> | >> >
> | >> > I have just discovered an extremely strange behaviour in conversion of
> | >> > an R logical to a C++ bool. Consider the minimal example:
> | >> >
> | >> > --- snip ---
> | >> >
> | >> > library(Rcpp)
> | >> > library(inline)
> | >> >
> | >> > ## this compiles and loads fine, but is wrong:
> | >> > wrong<- cxxfunction(signature(x="list") , '
> | >> >          List input(x);
> | >> >          const bool a = input[0];
> | >> >          return wrap(a);
> | >> >          ' , plugin = "Rcpp")
> | >> >
> | >> > wrong(list(TRUE))
> | >> > wrong(list(FALSE))
> | >> >
> | >> > ## this is correct:
> | >> > correct<- cxxfunction(signature(x="list") , '
> | >> >          List input(x);
> | >> >          const bool a = as<bool>(input[0]);
> | >> >          return wrap(a);
> | >> >          ' , plugin = "Rcpp")
> | >> >
> | >> > correct(list(TRUE))
> | >> > correct(list(FALSE))
> | >> >
> | >> > --- snap ----
> | >> >
> | >> > In Rcpp 0.8.9 wrong(list(FALSE)) == TRUE, which is quite surprising to
> | >> > the user...
> | >> > Sorry if this already a known feature, but then I would be curious if
> | >> > this behaviour is really wished?
> | >> >
> | >> > Thanks in advance,
> | >> > best regards
> | >> >
> | >> > Daniel
> | > -- Romain Francois Professional R Enthusiast +33(0) 6 28 91 30 30
> | > http://romainfrancois.blog.free.fr |- http://bit.ly/fT2rZM : highlight
> | > 0.2-5 |- http://bit.ly/gpCSpH : Evolution of Rcpp code size `-
> | > http://bit.ly/hovakS : RcppGSL initial release 
> | 
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