Ensures that x respects several parameters
IntegerVector, of allowed length for x. Default is NULL, for not checking this parameter.
CharacterVector, of allowed classes of x. Default is NULL, for not checking this parameter.
CharacterVector, of allowed types of x. Default is NULL, for not checking this parameter.
of allowed values for x (will be passed to cpp_allowed). Default is NULL, for not checking this parameter.
CharacterVector, function to execute when mandatory parameters are not met. Default is "stop". Allowed are "stop","warning","message","return". fun is placed in cpp_assert() in order to check it is correct before being used in assert() function.