[Rd] Defining a `show` function breaks the print-ing of S4 object -- bug or expected?

[Paul Gilbert]

On 06/30/2015 11:33 AM, Duncan Murdoch wrote:
> 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.

These are two different problems aren't they? I can see that you might 
want to ensure that base::print() calls methods::show(), but forcing the 
default print to go to base::print(), rather than whatever print() is 
first on the search path, would seem like a real change of philosophy. 
What about all the other base functions that can be overridden by 
something in the global environment?

Paul
>
> 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
>>>
>>>
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>>
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