[R] an assert() function

[Duncan Murdoch]

On 12/02/2013 9:11 AM, Greg Minshall wrote:
> hi.  i've looked for (and not found) an assert() function.  needing one,
> i created the following (from stop()).  i'm posting it in case 1)
> someone sees a problem with this; and 2) someone else has a need.

stopifnot() might do what you want.

The tricky thing in writing this sort of function is handling vector 
inputs.  Sometimes x is a vector, and then you need to decide what to do 
with

assert(x > 0)

Yours will only test the first component and issue a warning; the base 
one will test all(x > 0).  But the base behaviour causes its own 
problems; one came up recently in that

stopifnot( ncol(x) > 1 )

will not stop if x is just a vector, because ncol(x) is NULL, so ncol(x) 
 > 1 is a length 0 vector, and all(ncol(x) > 1) is TRUE.

Duncan Murdoch

>
> cheers, Greg
> ----
> ## an assert mechanism...
> assert <- function (shouldbe, ...) {
>    if (!shouldbe) {
>      .Internal(stop(as.logical(TRUE),
>                     .makeMessage("assertion failure: ", ..., domain = NULL)))
>    }
> }
>
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