`c` on zero length `POSIXct` fails

[bart1]

I just got reported a bug in the move package. This is the result of a concatenation of an zero length POSIXct. This works perfectly well in base R and behaves like other vectors (e.g. c(numeric(0)). However when lubridate is loaded this now fails. As this error is new to me I assume it relates to recent changes in this package (probably: 1570baa ). I think this combining of zero length strings should not produce an error.

(a<-structure(numeric(0), class = c("POSIXct", "POSIXt"), tzone = "UTC"))
#> POSIXct of length 0
c(a)
#> POSIXct of length 0
require(lubridate)
#> Loading required package: lubridate
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union
a
#> POSIXct of length 0
c(a)
#> Error in class(xx) <- cl: attempt to set an attribute on NULL
sessionInfo()
#> R version 4.1.2 (2021-11-01)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 20.04.3 LTS
#> 
#> Matrix products: default
#> BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
#> LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0
#> 
#> locale:
#>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
#>  [3] LC_TIME=nl_NL.UTF-8        LC_COLLATE=en_US.UTF-8    
#>  [5] LC_MONETARY=nl_NL.UTF-8    LC_MESSAGES=en_US.UTF-8   
#>  [7] LC_PAPER=nl_NL.UTF-8       LC_NAME=C                 
#>  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#> [11] LC_MEASUREMENT=nl_NL.UTF-8 LC_IDENTIFICATION=C       
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] lubridate_1.8.0
#> 
#> loaded via a namespace (and not attached):
#>  [1] knitr_1.34      magrittr_2.0.1  rlang_0.4.12    fastmap_1.1.0  
#>  [5] fansi_0.5.0     stringr_1.4.0   styler_1.6.1    highr_0.9      
#>  [9] tools_4.1.2     xfun_0.27       utf8_1.2.2      withr_2.4.2    
#> [13] htmltools_0.5.2 ellipsis_0.3.2  yaml_2.2.1      digest_0.6.28  
#> [17] tibble_3.1.5    lifecycle_1.0.1 crayon_1.4.1    purrr_0.3.4    
#> [21] vctrs_0.3.8     fs_1.5.0        glue_1.4.2      evaluate_0.14  
#> [25] rmarkdown_2.11  reprex_2.0.1    stringi_1.7.5   compiler_4.1.2 
#> [29] pillar_1.6.4    generics_0.1.1  backports_1.2.1 pkgconfig_2.0.3

^{Created on 2021-11-15 by the reprex package (v2.0.1)}

[bart1]

Just to confirm I tried with the previous version of lubridate an that works fine:

(a<-structure(numeric(0), class = c("POSIXct", "POSIXt"), tzone = "UTC"))
#> POSIXct of length 0
c(a)
#> POSIXct of length 0
require(lubridate)
#> Loading required package: lubridate
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union
a
#> POSIXct of length 0
c(a)
#> POSIXct of length 0
sessionInfo()
#> R version 4.1.2 (2021-11-01)
#> Platform: x86_64-pc-linux-gnu (64-bit)
#> Running under: Ubuntu 20.04.3 LTS
#> 
#> Matrix products: default
#> BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
#> LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0
#> 
#> locale:
#>  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
#>  [3] LC_TIME=nl_NL.UTF-8        LC_COLLATE=en_US.UTF-8    
#>  [5] LC_MONETARY=nl_NL.UTF-8    LC_MESSAGES=en_US.UTF-8   
#>  [7] LC_PAPER=nl_NL.UTF-8       LC_NAME=C                 
#>  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#> [11] LC_MEASUREMENT=nl_NL.UTF-8 LC_IDENTIFICATION=C       
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices utils     datasets  methods   base     
#> 
#> other attached packages:
#> [1] lubridate_1.7.10
#> 
#> loaded via a namespace (and not attached):
#>  [1] Rcpp_1.0.7      knitr_1.34      magrittr_2.0.1  rlang_0.4.12   
#>  [5] fastmap_1.1.0   fansi_0.5.0     stringr_1.4.0   styler_1.6.1   
#>  [9] highr_0.9       tools_4.1.2     xfun_0.27       utf8_1.2.2     
#> [13] withr_2.4.2     htmltools_0.5.2 ellipsis_0.3.2  yaml_2.2.1     
#> [17] digest_0.6.28   tibble_3.1.5    lifecycle_1.0.1 crayon_1.4.1   
#> [21] purrr_0.3.4     vctrs_0.3.8     fs_1.5.0        glue_1.4.2     
#> [25] evaluate_0.14   rmarkdown_2.11  reprex_2.0.1    stringi_1.7.5  
#> [29] compiler_4.1.2  pillar_1.6.4    generics_0.1.1  backports_1.2.1
#> [33] pkgconfig_2.0.3

^{Created on 2021-11-15 by the reprex package (v2.0.1)}

[vspinu]

Thanks for diagnosing and reporting this. I indeed missed this corner case in that commit.