R Under development (unstable) (2024-07-28 r86931 ucrt) -- "Unsuffered Consequences"
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Platform: x86_64-w64-mingw32/x64

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> message("*** debug() ...")
*** debug() ...
> 
> debug <- startup:::debug ## non-exported
> is_debug_on <- startup::is_debug_on
> 
> print(debug())
[1] FALSE
> print(is_debug_on())
[1] FALSE
> 
> print(debug(TRUE))
[1] TRUE
> stopifnot(is_debug_on())
> 
> startup:::log("Hello")
0.000s: Hello
> startup:::logf("Hello %s", "world")
0.000s: Hello world
> startup:::logp(str(1:10))
0.004s:  int [1:10] 1 2 3 4 5 6 7 8 9 10
0.004s: NULL
> 
> print(debug(FALSE))
[1] FALSE
> stopifnot(!is_debug_on())
> 
> message("*** debug() ... DONE")
*** debug() ... DONE
> 
> rm(list = "debug")
> 
> proc.time()
   user  system elapsed 
   0.12    0.04    0.17