condition: Conditions

In cnd: Create and Register Conditions

Conditions

Description

condition() is used to create a new condition function that itself returns a new condition.

conditions() retrieves all conditions based on search values. The parameters serve as filtering arguments.

Usage

condition(
  class,
  message = NULL,
  type = c("condition", "message", "warning", "error"),
  package = get_package(),
  exports = NULL,
  help = NULL,
  registry = package,
  register = !is.null(registry)
)

conditions(
  ...,
  class = NULL,
  type = NULL,
  package = NULL,
  registry = NULL,
  fun = NULL
)

cond(x)

cnd(condition)

conditions(x, ...) <- value

## S3 replacement method for class ''function''
conditions(x, append = FALSE, ...) <- value

## S3 replacement method for class ''cnd::condition_progenitor''
conditions(x, ...) <- value

Arguments

class	The name of the new class
message	The message to be displayed when the condition is called. When entered as a character vector, the message is collapsed into a single string. Use explicit line returns to generate new lines in output messages. When a function is used and a character vector returned, each element is treated as a new line.
type	The type of condition: error, warning, or message
package	The package to which the condition belongs
exports	The exported functions to be displayed when the condition is called
help	The help message to be displayed for the condition function
registry	The name of the registry to store the condition
register	Controls registration checks
...	Additional arguments passed to methods
fun	if a function is passed, then retrieves the "conditions" attribute
x	An object
condition	A condition_generator object
value	A condition
append	If TRUE, adds to the conditions attribute

Details

Conditions

Value

• condition() a condition_generator object

• conditions() a list of condition_generator objects

• cond() A condition_generator object

• cnd() is a wrapper for calling stop(), warning(), or message(); when condition is a type, an error is thrown, and likewise for the other types. When an error isn't thrown, the condition is returned, invisibly.

condition_generator

A condition_generator is an object (a special function) which can be used to create generate a new condition, based on specifications applied in condition(). These functions use ... to absorb extra arguments and contain a special .call parameter. By default, .call captures the parent call from where the condition_generator was created, but users may pass their own call to override this. See call. in conditionCall()

condition() conditions

Conditions are generated through the {cnd} package. The following conditions are associated with this function:

cnd:as_character_cnd_error/error

You cannot coerce a condition_generator object to a character. This may have occurred when trying to put a condition function through stop() or warning. Instead, call the function first, then pass the result to stop() or warning().

For example:

# Instead of this
stop(my_condition)

# Do this
stop(my_condition())

cnd:condition_message_generator/error

condition_generator objects are not conditions. You may have made this mistake:

x <- condition("my_condition")
conditionMessage(x)

Condition generators need to be called first before they can be used as conditions. Try this instead:

x <- condition("my_condition")
conditionMessage(x())

cnd:condition_overwrite/warning

cnd:invalid_condition/error

The class, exports, and help parameters must be a single character string. If you are passing a function, it must be a valid function.

cnd:invalid_condition_message/error

Conditions messages are displayed when invoked through conditionMessage(). You can set a static message by passing through a character vector, or a dynamic message by passing through a function. The function should return a character vector.

When message is not set, a default "there was an error" message is used.

cnd:match_arg/error

Mostly match.arg() but with a custom condition

cnd:no_package_exports/warning

The exports parameter requires a package

For more conditions, see: cnd-cnd-conditions

cnd() conditions

Conditions are generated through the {cnd} package. The following conditions are associated with this function:

cnd:cond_cnd_class/error

cnd() simple calls the appropriate function: stop(), warning(), or message() based on the type parameter from condition().

For more conditions, see: cnd-cnd-conditions

See Also

cnd-package

Examples

# create a new condition:
cond_bad_value <- condition("bad_value", type = "error")

# use the condition
try(stop(cond_bad_value()))
try(cnd(cond_bad_value()))

# dynamic messages:
cond_class_error <- condition(
  "class_error",
  message = function(x) paste("class cannot be", toString(class(x))),
  type = "error"
)
try(stop(cond_class_error(list())))

cnd documentation built on April 3, 2025, 9:43 p.m.