Henrik Bengtsson
2025-Oct-08 15:43 UTC
[Rd] Is structure(NA, class = c("def", "condition")) a valid 'condition' object?
Thank you, Duncan. It sounds like you're reading it the same as I, i.e. what typeof(<condition>) should be is not specified. Using list() in my tiny example was a thinko - NULL would indeed have been better. /Henrik On Wed, Oct 8, 2025 at 5:32?AM Duncan Murdoch <murdoch.duncan at gmail.com> wrote:> > Besides `conditionMessage` and `conditionCall`, base R also has methods > defined for `as.character` and `print`, but they appear to make no > assumptions about the object other than having `conditionMessage` and > `conditionCall` defined. > > The help page is silent about what type of thing `conditionCall()` > should return, but the objects produced by the standard condition > functions will return the `call` argument, which defaults to `NULL`, but > could be a "call expression". > > So I'm not sure your definition of the `conditionCall()` methods is > going to work: `list()` doesn't return an expression. Returning > `NULL` would be better. > > Of course, in S3 "valid" isn't defined formally; it just means something > that won't mess up. So it's quite possible `list()` is okay. > > Duncan Murdoch > > > On 2025-10-07 7:42 p.m., Henrik Bengtsson wrote: > > I think structure(NA, class = c("def", "condition")) is a valid > > 'condition' object. Am I wrong? > > > > BACKGROUND: > > > > The abstract 'condition' class: why type or mode can a 'condition' object have? > > > > In help("condition"), we can read that: > > > > "Conditions are objects inheriting from the abstract class condition. ..." > > > > and then it specifies the API, i.e. the methods it should support, e.g. > > > > "The functions conditionMessage and conditionCall are generic > > functions that return the message and call of a condition." > > > > Then we have several functions for creating 'condition' objects, e.g. > > > >> simpleCondition > > function (message, call = NULL) > > { > > class <- c("simpleCondition", "condition") > > structure(list(message = as.character(message), call = call), > > class = class) > > } > > > > AFAIK, all of them create 'condition' object of type 'list'. > > > > > > CAN CONDITIONS BE ENVIRONMENTS OR ATOMIC OBJECTS? > > > > However, is the list type a requirement? I cannot find it specified > > anywhere. The way I interpret help("condition") and how it is > > carefully written using terms like "abstract class" and not mentioning > > the type anywhere, I take it as: > > > > cnd1 <- structure(new.env(), class = c("abc", "condition")) > > > > and > > > > cnd2 <- structure(NA, class = c("def", "condition")) > > > > are both valid 'condition' objects, as long as we define the S3 > > methods for `conditionMessage()` and `conditionCall()`, e.g. > > > > conditionMessage.abc <- function(c) "boom" > > conditionCall.abc <- function(c) list() > > > > conditionMessage.def <- function(c) "boom" > > conditionCall.def <- function(c) list() > > > > FWIW, I create 'condition' objects of type NA in my 'R.oo' package > > going back ~25 years. > > > > Thanks, > > > > Henrik > > > > ______________________________________________ > > R-devel at r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel >
Tim Taylor
2025-Oct-22 23:04 UTC
[Rd] Is structure(NA, class = c("def", "condition")) a valid 'condition' object?
FWIW - I read this the same way as you Henrik. I presume if there was a desire to restrict the underlying typeof the condition a dedicated constructor would have been supplied and the type enforced. Whether this would be better or worse is an interesting thing to ponder. Tim> On 8 Oct 2025, at 16:43, Henrik Bengtsson <henrik.bengtsson at gmail.com> wrote: > > ?Thank you, Duncan. > > It sounds like you're reading it the same as I, i.e. what > typeof(<condition>) should be is not specified. > > Using list() in my tiny example was a thinko - NULL would indeed have > been better. > > /Henrik > >> On Wed, Oct 8, 2025 at 5:32?AM Duncan Murdoch <murdoch.duncan at gmail.com> wrote: >> >> Besides `conditionMessage` and `conditionCall`, base R also has methods >> defined for `as.character` and `print`, but they appear to make no >> assumptions about the object other than having `conditionMessage` and >> `conditionCall` defined. >> >> The help page is silent about what type of thing `conditionCall()` >> should return, but the objects produced by the standard condition >> functions will return the `call` argument, which defaults to `NULL`, but >> could be a "call expression". >> >> So I'm not sure your definition of the `conditionCall()` methods is >> going to work: `list()` doesn't return an expression. Returning >> `NULL` would be better. >> >> Of course, in S3 "valid" isn't defined formally; it just means something >> that won't mess up. So it's quite possible `list()` is okay. >> >> Duncan Murdoch >> >> >>> On 2025-10-07 7:42 p.m., Henrik Bengtsson wrote: >>> I think structure(NA, class = c("def", "condition")) is a valid >>> 'condition' object. Am I wrong? >>> >>> BACKGROUND: >>> >>> The abstract 'condition' class: why type or mode can a 'condition' object have? >>> >>> In help("condition"), we can read that: >>> >>> "Conditions are objects inheriting from the abstract class condition. ..." >>> >>> and then it specifies the API, i.e. the methods it should support, e.g. >>> >>> "The functions conditionMessage and conditionCall are generic >>> functions that return the message and call of a condition." >>> >>> Then we have several functions for creating 'condition' objects, e.g. >>> >>>> simpleCondition >>> function (message, call = NULL) >>> { >>> class <- c("simpleCondition", "condition") >>> structure(list(message = as.character(message), call = call), >>> class = class) >>> } >>> >>> AFAIK, all of them create 'condition' object of type 'list'. >>> >>> >>> CAN CONDITIONS BE ENVIRONMENTS OR ATOMIC OBJECTS? >>> >>> However, is the list type a requirement? I cannot find it specified >>> anywhere. The way I interpret help("condition") and how it is >>> carefully written using terms like "abstract class" and not mentioning >>> the type anywhere, I take it as: >>> >>> cnd1 <- structure(new.env(), class = c("abc", "condition")) >>> >>> and >>> >>> cnd2 <- structure(NA, class = c("def", "condition")) >>> >>> are both valid 'condition' objects, as long as we define the S3 >>> methods for `conditionMessage()` and `conditionCall()`, e.g. >>> >>> conditionMessage.abc <- function(c) "boom" >>> conditionCall.abc <- function(c) list() >>> >>> conditionMessage.def <- function(c) "boom" >>> conditionCall.def <- function(c) list() >>> >>> FWIW, I create 'condition' objects of type NA in my 'R.oo' package >>> going back ~25 years. >>> >>> Thanks, >>> >>> Henrik >>> >>> ______________________________________________ >>> R-devel at r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-devel >> > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel