On 30/08/2018, 20:15, "R-devel on behalf of Hadley Wickham"
<[email protected] on behalf of [email protected]> wrote:
On Thu, Aug 30, 2018 at 10:58 AM Martin Maechler
<[email protected]> wrote:
>
> >>>>> Joris Meys
> >>>>> on Thu, 30 Aug 2018 14:48:01 +0200 writes:
>
> > On Thu, Aug 30, 2018 at 2:09 PM Dénes Tóth
> > <[email protected]> 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.
Can you explain your reasoning a bit more here? I'd like to understand
the general principle, because from my perspective it's more
parsimonious to say that the inputs to || and && must be length 1,
rather than to say that inputs could be length 0 or length 1, and in
the length 0 case they are replaced with NA.
Hadley
I would say the value NA would cause warnings later on, that are easy to track
down, so a return of NA is far less likely to cause problems than an unintended
TRUE or FALSE. And I guess there would be some code reliant on 'logical(0) ||
TRUE' returning TRUE, that wouldn't necessarily be a mistake.
But I think it's hard to predict how exactly people are using functions. I
personally can't imagine a situation where I'd use || or && outside an
if-statement, so I'd rather have the current behaviour, because I'm not sure if
I'm reliant on logical(0) || TRUE somewhere in my code (even though that would
be ugly code, it's not wrong per se)
But I could always rewrite it, so I believe it's more a question of how much
would have to be rewritten. Maybe implement it first in devel, to see how many
people would complain?
Emil Bode
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