catch_cnd() should take class argument

[lionel-]

And probably throw an error when a condition of the excepted class failed to be caught, instead of returning NULL. This way it can safely be used in unit tests and other situations where you expect a condition. WDYT @hadley?

[hadley]

Hmmm, I like the current interface. What you're describing seems more like a special purpose function that should be part of testthat.

[lionel-]

How about just taking an optional condition class defaulting to "condition" then? If not caught, return NULL. There's currently no easy way to catch a condition whose class is in a variable. Then the testthat helper can be implemented around catch_cnd().

catch_cnd <- function(expr, class = "condition") {
  stopifnot(is_string(class))
  handler <- set_names(list(identity), class)

  value(
    tryCatch(!!!handler, {
      force(expr)
      return(NULL)
    })
  )
}

It feels like catch_cnd() is not complete in its current state, at least for programming where the caller invariably has to check for the condition type in addition to checking for NULL.

[hadley]

Yeah, I like that.