From murdoch.duncan at gmail.com  Tue Jun 30 17:33:52 2015
From: murdoch.duncan at gmail.com (Duncan Murdoch)
Date: Tue, 30 Jun 2015 17:33:52 +0200
Subject: [Rd] Defining a `show` function breaks the print-ing of S4
 object -- bug or expected?
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Message-ID: <5592B6E0.30009@gmail.com>

On 30/06/2015 5:27 PM, Lorenz, David wrote:
> There is something I'm really missing here. The function show is a
> standardGeneric function, so the correct way to write it as method like
> this:

That describes methods::show.  The problem is that the default print
mechanism isn't calling methods::show() (or base::print() as Luke says),
it's calling show() or print() in the global environment, so the user's
function overrides the generic, and you get the error.

Luke, are you going to look at this, or should I?

Duncan Murdoch

> 
> setMethod("show",  "Person", function(object) {
> 
> for an object of class "Person" for example.


> Dave
> 
> On Tue, Jun 30, 2015 at 10:11 AM, <luke-tierney at uiowa.edu> wrote:
> 
>> Same thing happens with S3 if you redefine print(). I thought that
>> code was actually calculating the function to call rather than the
>> symbol to use, but apparently not. Shouldn't be too hard to fix.
>>
>> luke
>>
>> On Tue, 30 Jun 2015, Hadley Wickham wrote:
>>
>>  On Tue, Jun 30, 2015 at 2:20 PM, Duncan Murdoch
>>> <murdoch.duncan at gmail.com> wrote:
>>>
>>>> On 30/06/2015 1:57 PM, Hadley Wickham wrote:
>>>>
>>>>> A slightly simpler formulation of the problem is:
>>>>>
>>>>> show <- function(...) stop("My show!")
>>>>> methods::setClass("Person", slots = list(name = "character"))
>>>>> methods::new("Person", name = "Tom")
>>>>> #> Error in (function (...)  : My show!
>>>>>
>>>>
>>>> Just to be clear:  the complaint is that the auto-called show() is not
>>>> methods::show?  I.e. after
>>>>
>>>> x <- methods::new("Person", name = "Tom")
>>>>
>>>> you would expect
>>>>
>>>> show(x)
>>>>
>>>> to give the error, but not
>>>>
>>>> x
>>>>
>>>> ??
>>>>
>>>
>>> Correct - I'd expect print() to always call methods::show(), not
>>> whatever show() is first on the search path.
>>>
>>> Hadley
>>>
>>>
>>>
>> --
>> Luke Tierney
>> Ralph E. Wareham Professor of Mathematical Sciences
>> University of Iowa                  Phone:             319-335-3386
>> Department of Statistics and        Fax:               319-335-3017
>>    Actuarial Science
>> 241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
>> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu
>>
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
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[Rd] Defining a `show` function breaks the print-ing of S4 object -- bug or expected?
Duncan Murdoch