setattr() creates a deep copy of the attribute object

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data, performance

Research direction

Start with the setattr() entry point and reproduce the address comparisons in the issue using R. Trace how the attribute is assigned, then add coverage showing that the attribute object is not copied while the requested reference behavior is preserved.

Written by the indexing model from the issue text.

Description

by-reference

I recently realized that the setattr function changes the input object by reference (that is, without any copy), however, it copies the attribute object:

library(data.table)
x <- 1
a1 <- "an attribute object which can be a large vector"
orig_addresses <- c(address(x), address(a1))
data.table::setattr(x, "a", a1)
new_addresses <- c(address(x), address(attr(x, "a")))
orig_addresses == new_addresses
# [1] TRUE FALSE

The base solution does exactly the opposite: it copies the input object, but does not copy the attribute object:

library(data.table)
x <- 1
a1 <- "an attribute object which can be a large vector"
orig_addresses <- c(address(x), address(a1))
attr(x, "a") <- a1
new_addresses <- c(address(x), address(attr(x, "a")))
orig_addresses == new_addresses
# [1] FALSE TRUE

The bit package also has a setattr function which does not create any copy:

library(data.table)
library(bit)
x <- 1
a1 <- "an attribute object which can be a large vector"
orig_addresses <- c(address(x), address(a1))
bit::setattr(x, "a", a1)
new_addresses <- c(address(x), address(attr(x, "a")))
orig_addresses == new_addresses
# [1] TRUE TRUE

Would it be possible to the modify the setattr function so that it does not create a copy of the attribute object?

sessionInfo()
R version 3.2.1 (2015-06-18)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Linux Mint LMDE

locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats graphics grDevices utils datasets methods base

other attached packages:
[1] bit_1.1-12 data.table_1.9.5

loaded via a namespace (and not attached):
[1] tools_3.2.1 chron_2.3-45

Dominant language
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