From emil@bode @ending from d@n@@kn@w@nl  Fri Aug 31 11:48:57 2018
From: emil@bode @ending from d@n@@kn@w@nl (Emil Bode)
Date: Fri, 31 Aug 2018 09:48:57 +0000
Subject: [Rd] ROBUSTNESS: x || y and x && y to give warning/error if
 length(x) != 1 or length(y) != 1
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?On 30/08/2018, 20:15, "R-devel on behalf of Hadley Wickham" <r-devel-bounces at r-project.org on behalf of h.wickham at gmail.com> wrote:

    On Thu, Aug 30, 2018 at 10:58 AM Martin Maechler
    <maechler at stat.math.ethz.ch> wrote:
    >
    > >>>>> Joris Meys
    > >>>>>     on Thu, 30 Aug 2018 14:48:01 +0200 writes:
    >
    >     > On Thu, Aug 30, 2018 at 2:09 PM D?nes T?th
    >     > <toth.denes at 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.
    
    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


    



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