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
`!` 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
I'm just curious. Why making "if" generic is even more dangerous? Best, Da On Sat, Mar 4, 2017 at 1:22 PM, G?bor Cs?rdi <csardi.gabor at gmail.com> wrote:> `!` 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