R: Check if an argument is a function

checkFunction {checkmate} | R Documentation

## Check if an argument is a function

### Description

Check if an argument is a function

### Usage

    checkFunction(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

    check_function(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

    assertFunction(
      x,
      args = NULL,
      ordered = FALSE,
      nargs = NULL,
      null.ok = FALSE,
      .var.name = vname(x),
      add = NULL
    )

    assert_function(
      x,
      args = NULL,
      ordered = FALSE,
      nargs = NULL,
      null.ok = FALSE,
      .var.name = vname(x),
      add = NULL
    )

    testFunction(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

    test_function(x, args = NULL, ordered = FALSE, nargs = NULL, null.ok = FALSE)

    expect_function(
      x,
      args = NULL,
      ordered = FALSE,
      nargs = NULL,
      null.ok = FALSE,
      info = NULL,
      label = vname(x)
    )

### Arguments

`x` | [any] Object to check.
`args` | [`character`] Expected formal arguments. Checks that a function has no arguments if set to `character(0)`. Default is `NULL` (no check).
`ordered` | [`logical(1)`] Flag whether the arguments provided in `args` must be the first `length(args)` arguments of the function in the specified order. Default is `FALSE`.
`nargs` | [`integer(1)`] Required number of arguments, without `...`. Default is `NULL` (no check).
`null.ok` | [`logical(1)`] If set to `TRUE`, `x` may also be `NULL`. In this case only a type check of `x` is performed, all additional checks are disabled.
`.var.name` | [`character(1)`] Name of the checked object to print in assertions. Defaults to the heuristic implemented in `vname`.
`add` | [`AssertCollection`] Collection to store assertion messages. See `AssertCollection`.
`info` | [character(1)] Extra information to be included in the message for the testthat reporter. See `expect_that`.
`label` | [`character(1)`] Name of the checked object to print in messages. Defaults to the heuristic implemented in `vname`.

### Value

Depending on the function prefix: If the check is successful, the functions `assertFunction`/`assert_function` return `x` invisibly, whereas `checkFunction`/`check_function` and `testFunction`/`test_function` return `TRUE`. If the check is not successful, `assertFunction`/`assert_function` throws an error message, `testFunction`/`test_function` returns `FALSE`, and `checkFunction` returns a string with the error message. The function `expect_function` always returns an `expectation`.

### See Also

Other basetypes: `checkArray()`, `checkAtomicVector()`, `checkAtomic()`, `checkCharacter()`, `checkComplex()`, `checkDataFrame()`, `checkDate()`, `checkDouble()`, `checkEnvironment()`, `checkFactor()`, `checkFormula()`, `checkIntegerish()`, `checkInteger()`, `checkList()`, `checkLogical()`, `checkMatrix()`, `checkNull()`, `checkNumeric()`, `checkPOSIXct()`, `checkRaw()`, `checkVector()`

### Examples

    testFunction(mean)
    testFunction(mean, args = "x")

[Package checkmate version 2.0.0 Index]