[R-pkg-devel] [FORGED] Re: Help on Windows CRAN Check

[Rolf Turner]

On 5/03/20 9:04 pm, Tomas Kalibera wrote:

> On 3/5/20 4:26 AM, John Lawson wrote:
>> I see this error on the CRAN Check report

<SNIP>

>> Fatal error: the condition has length > 1
> 
> The problem is that the condition t1 == "I" & t2 == "(" of the if
> statement in the code is not a scalar. Even though this has been allowed
> in R historically, the first element has been used, it is almost always
> a sign of coding error, so it is going to become a runtime error.
> 
> So what one should do is fix the code to only use scalar conditions -
> ensure t1, t2 are scalar, replace & by &&.

Perhaps I'm being even thicker than usual (imagine that!) but I don't 
grok that last recommendation:  "replace & by &&".  It's usually 
harmless but indicates a lack of understanding.  The "&&" operator 
evaluates the second condition only if the first condition is TRUE.  It 
is useful (only) in setting where the second condition is meaningful 
only when the first condition is TRUE.

Things like:

    if(!is.null(x) && x > 0)

If "x" were null then the second  condition would cause an error to be 
thrown if you used "&" rather than "&&".

In all (???) situations where "&&" works, then "&" works as well. 
However it's a Good Idea to use the language as intended.

It I'm missing some point here, please enlighten me.

<SNIP>

cheers,

Rolf

-- 
Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276