[Rd] readChar() could read the whole file by default?

[Michael Chirico]

I am curious why readLines() has a default (n=-1L) to read the full
file while readChar() has no default for nchars= (i.e., readChar(file)
is an error). Is there a technical reason for this?

I often[1] see code like paste(readLines(f), collapse="\n") which
would be better served by readChar(), especially given issues with the
global string cache I've come across[2]. But lacking the default, the
replacement might come across less clean.

For my own purposes the incantation readChar(file, file.size(file)) is
ubiquitous. Taking CRAN code[3] as a sample[4], 41% of readChar()
calls use either readChar(f, file.info(f)$size) or readChar(f,
file.size(f))[5].

Thanks for the consideration and feedback,
Mike C

[1] e.g. a quick search shows O(100) usages in CRAN packages:
https://github.com/search?q=org%3Acran+%2Fpaste%5B%28%5D%5Cs*readLines%5B%28%5D.*%5B%29%5D%2C%5Cs*collapse%5Cs*%3D%5Cs*%5B%27%22%5D%5B%5C%5C%5D%2F+lang%3AR&type=code,
and O(1000) usages generally on GitHub:
https://github.com/search?q=lang%3AR+%2Fpaste%5B%28%5D%5Cs*readLines%5B%28%5D.*%5B%29%5D%2C%5Cs*collapse%5Cs*%3D%5Cs*%5B%27%22%5D%5B%5C%5C%5D%2F+lang%3AR&type=code
[2] AIUI the readLines() approach "pollutes" the global string cache
with potentially 1000s/10000s of strings for each line, only to get
them gc()'d after combining everything with paste(collapse="\n")
[3] The mirror on GitHub, which includes archived packages as well as
current (well, eventually-consistent) versions.
[4] Note that usage in packages is likely not representative of usage
in scripts, e.g. I often saw readChar(f, 1), or eol-finders like
readChar(f, 500) + grep("[\n\r]"), which makes more sense to me as
something to find in package internals than in analysis scripts. FWIW
I searched an internal codebase (scripts and packages) and found 70%
of usages reading the full file.
[5] repro: https://gist.github.com/MichaelChirico/247ea9500460dca239f031e74bdcf76b
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