From csardi.gabor at gmail.com  Sat Mar  4 19:22:35 2017
From: csardi.gabor at gmail.com (=?UTF-8?B?R8OhYm9yIENzw6FyZGk=?=)
Date: Sat, 4 Mar 2017 18:22:35 +0000
Subject: [Rd] can we override "if" in R?
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`!` is a generic, `if` is not. You can define an `if` that is generic,
but this might be even more dangerous....

? `if` <- function(a, b, c) UseMethod("if")
? `if.default` <- function(a,b,c) base::`if`(a, b, c)
? `if.foo` <- function(a, b, c) FALSE
? a <- structure(42, class = "foo")

? if (a) TRUE else FALSE
[1] FALSE

? if (1) TRUE else FALSE
[1] TRUE

Gabor

On Sat, Mar 4, 2017 at 5:47 PM, Da Zheng <zhengda1936 at gmail.com> wrote:
> Thanks.
> Can I override it for a specific class?
> I can do that for operators such as "!". For example, "!.fm" works for
> objects of the class "fm".
> It seems I can't do the same for "if".
>
> Best,
> Da
>
> On Sat, Mar 4, 2017 at 12:41 PM, G?bor Cs?rdi <csardi.gabor at gmail.com> wrote:
>> You can. Perhaps needless to say, be careful with this.
>>
>> ? `if` <- function(...) FALSE
>> ? if (TRUE) TRUE else FALSE
>> [1] FALSE
>>
>> G.
>>
>> On Sat, Mar 4, 2017 at 5:36 PM, Da Zheng <zhengda1936 at gmail.com> wrote:
>>> Hello,
>>>
>>> I heard we can override almost everything in R. Is it possible to
>>> override "if" keyword in R to evaluate my own object instead of a
>>> logical value?
>>>
>>> Thanks,
>>> Da
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel



[Rd] can we override "if" in R?
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