is class2 Parameter's Documentation is Ambiguous

Good day,

It appears that class2 needs to be of length 1.
is(4, c("data.frame", "DataFrame"))
Error in is(4, c("data.frame", "DataFrame")) : 
  length(class2) == 1L is not TRUE

However, the documentation is "class1, class2: character strings giving the names of each of the two classes between which is relations are to be examined"

Also, class1 is not a parameter of the is function. It is a parameter of the extends function. I think the mention of "is relations" is unintended. Can the documenation be rewritten to remove the ambiguity for these?

--------------------------------------
Dario Strbenac
University of Sydney
Camperdown NSW 2050
Australia
Dear Dario,

You misunderstood the documentation of is(). class1 refers to extends().
is() only uses class2, not class1.

I'd use inherits(your_object, "DataFrame") and inherits(your_object,
"data.frame"). The latter is probably redundant.

Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND
FOREST
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx at inbo.be
Havenlaan 88 bus 73, 1000 Brussel
www.inbo.be

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Op di 16 aug. 2022 om 12:01 schreef Dario Strbenac via R-devel <
r-devel at r-project.org>:
Good day,

It appears that class2 needs to be of length 1.

is(4, c("data.frame", "DataFrame"))
Error in is(4, c("data.frame", "DataFrame")) :
  length(class2) == 1L is not TRUE

However, the documentation is "class1, class2: character strings giving
the names of each of the two classes between which is relations are to be
examined"

Also, class1 is not a parameter of the is function. It is a parameter of
the extends function. I think the mention of "is relations" is unintended.
Can the documenation be rewritten to remove the ambiguity for these?

--------------------------------------
Dario Strbenac
University of Sydney
Camperdown NSW 2050
Australia
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