R devel - Jun 2019 - Could generic functions check different S3 methods for an object when one of them produces an error?

Hi,


Let's say one has an object with multiple classes, and a generic function to
apply to it has associated S3 methods for more than one of those classes.
Further, the method it chooses (I do not know how; some order in the class
vector?) is not the suitable one and it produces an error. Would there be some
way to make the generic function to choice the correct method, or in case that
for any method taken it produces an error, to try another one.


For example (commented in detail
here<https://github.com/tidymodels/broom/issues/714>):


# object with multiple classes: the output of function `geepack::geeglm`. The
output of `class(object)`:

```

[1] "geeglm" "gee" "glm" "lm"

```

The generic function: `stats::confint`.

The S3 method chosen: `confint.glm`. It produces an error. The correct method in
this case would be `broom:::confint.geeglm`.


Thank you!

Iago

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On 17/06/2019 3:56 a.m., IAGO GIN? V?ZQUEZ wrote:
> Hi,
> 
> 
> Let's say one has an object with multiple classes, and a generic
function to apply to it has associated S3 methods for more than one of those
classes. Further, the method it chooses (I do not know how; some order in the
class vector?) is not the suitable one and it produces an error. Would there be
some way to make the generic function to choice the correct method, or in case
that for any method taken it produces an error, to try another one.
> 
> 
> For example (commented in detail
here<https://github.com/tidymodels/broom/issues/714>):
> 
> 
> # object with multiple classes: the output of function `geepack::geeglm`.
The output of `class(object)`:
> 
> ```
> 
> [1] "geeglm" "gee" "glm" "lm"
> 
> ```
> 
> The generic function: `stats::confint`.
> 
> The S3 method chosen: `confint.glm`. It produces an error. The correct
method in this case would be `broom:::confint.geeglm`.
There is something wrong here.  If R knows about confint.geeglm (because 
broom is loaded, for example), then confint(x) should call it before it 
calls confint.glm.  It will look for methods confint.geeglm, then 
confint.gee, then confint.glm, then confint.lm.

However, when I run your code and load broom, I see

 > methods("confint")
[1] confint.default  confint.glm*     confint.lm       confint.lme* 
confint.lmList*  confint.nls*     confint.nlsList*
see '?methods' for accessing help and source code


(with no confint.geeglm shown).  So something is wrong, probably in 
broom.  As far as I can see, it never declares confint.geeglm as an 
S3method in its NAMESPACE file.  (I'm looking at the devel version in 
https://github.com/tidymodels/broom/blob/master/NAMESPACE).

Get that fixed, and your problem should go away.

Duncan Murdoch