is_flag_advanced {assertions}

Check if x is a flag

Description

This function is designed for use with assert_create_advanced. It must return TRUE for the assertion to pass or a string representing the error message if the assertion should fail.

Usage

is_flag_advanced(x)

Arguments

x

A value to be checked

Value

Returns invisible(TRUE) if x is a logical value with length 1. Returns a string with an error message if x is not a logical value or has a length other than 1.