[Rd] Should last default to .Machine$integer.max-1 for substring()

[Martin Maechler]

>>>>> Tomas Kalibera 
>>>>>     on Mon, 21 Jun 2021 10:08:37 +0200 writes:

    > On 6/21/21 9:35 AM, Martin Maechler wrote:
    >>>>>>> Michael Chirico
    >>>>>>> on Sun, 20 Jun 2021 15:20:26 -0700 writes:
    >> > Currently, substring defaults to last=1000000L, which
    >> > strongly suggests the intent is to default to "nchar(x)"
    >> > without having to compute/allocate that up front.
    >> 
    >> > Unfortunately, this default makes no sense for "very
    >> > large" strings which may exceed 1000000L in "width".
    >> 
    >> Yes;  and I tend to agree with you that this default is outdated
    >> (Remember :  R was written to work and run on 2 (or 4?) MB of RAM on the
    >> student lab  Macs in Auckland in ca 1994).
    >> 
    >> > The max width of a string is .Machine$integer.max-1:
    >> 
    >> (which Brodie showed was only almost true)
    >> 
    >> > So it seems to me either .Machine$integer.max or
    >> > .Machine$integer.max-1L would be a more sensible default. Am I missing
    >> > something?
    >> 
    >> The "drawback" is of course that .Machine$integer.max  is still
    >> a function call (as R beginners may forget) contrary to <nnnnn>L,
    >> but that may even be inlined by the byte compiler (? how would we check ?)
    >> and even if it's not, it does more clearly convey the concept
    >> and idea  *and* would probably even port automatically if ever
    >> integer would be increased in R.

    > We still have the problem that we need to count characters, not bytes, 
    > if we want the default semantics of "until the end of the string".

    > I think we would have to fix this either by really using 
    > "nchar(type="c"))" or by using e.g. NULL and then treating this as a 
    > special case, that would be probably faster.

    > Tomas

You are right, as always, Tomas.
I agree that would be better and we should do it if/when we change
the default there.

Martin