#' Extract class as a single string.
#'
#' @param x any object.
class0 <- function(x)collapse(class(x), '/')
#' Check if a regular expression is valid.
#'
#' @param pattern the regular expression pattern to test.
is_valid_regex <- function(pattern){
tryCatch( grepl(pattern, '') || TRUE
, error= function(e)structure(FALSE, msg=e$message))
}
if(FALSE){#@testing
expect_true(is_valid_regex("^hello world$"))
expect_false(is_valid_regex("^hello (world$"))
expect_identical( validate_that(is_valid_regex("^hello (world$"))
, "invalid regular expression " %<<<%
"'^hello (world$', reason 'Missing ')''"
)
}
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