[Rd] ROBUSTNESS: x || y and x && y to give warning/error if length(x) != 1 or length(y) != 1

Martin Maechler m@echler @ending from @t@t@m@th@ethz@ch
Thu Aug 30 17:58:17 CEST 2018

>>>>> Joris Meys 
>>>>>     on Thu, 30 Aug 2018 14:48:01 +0200 writes:

    > On Thu, Aug 30, 2018 at 2:09 PM Dénes Tóth
    > <toth.denes using kogentum.hu> wrote:
    >> Note that `||` and `&&` have never been symmetric:
    >> TRUE || stop() # returns TRUE stop() || TRUE # returns an
    >> error
    > Fair point. So the suggestion would be to check whether x
    > is of length 1 and whether y is of length 1 only when
    > needed. I.e.

    > c(TRUE,FALSE) || TRUE

    > would give an error and

    > TRUE || c(TRUE, FALSE)

    > would pass.

    > Thought about it a bit more, and I can't come up with a
    > use case where the first line must pass. So if the short
    > circuiting remains and the extra check only gives a small
    > performance penalty, adding the error could indeed make
    > some bugs more obvious.

I agree "in theory".
Thank you, Henrik, for bringing it up!

In practice I think we should start having a warning signalled.
I have checked the source code in the mean time, and the check
is really very cheap
{ because it can/should be done after checking isNumber(): so
  then we know we have an atomic and can use XLENGTH() }

The 0-length case I don't think we should change as I do find
NA (is logical!) to be an appropriate logical answer.

Martin Maechler
ETH Zurich and R Core team.

    > Cheers Joris

    > -- 
    > Joris Meys Statistical consultant

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