[Rd] binary form of is() contradicts its unary form

[Hervé Pagès]

Hi,

The unary forms of is() and extends() report that data.frame
extends list, oldClass, and vector:

   > is(data.frame())
   [1] "data.frame" "list"       "oldClass"   "vector"

   > extends("data.frame")
   [1] "data.frame" "list"       "oldClass"   "vector"

However, the binary form of is() disagrees:

   > is(data.frame(), "list")
   [1] FALSE
   > is(data.frame(), "oldClass")
   [1] FALSE
   > is(data.frame(), "vector")
   [1] FALSE

while the binary form of extends() agrees:

   > extends("data.frame", "list")
   [1] TRUE
   > extends("data.frame", "oldClass")
   [1] TRUE
   > extends("data.frame", "vector")
   [1] TRUE

Who is right?

Shouldn't 'is(object, class2)' be equivalent
to 'class2 %in% is(object)'? Furthermore, is there
any reason why 'is(object, class2)' is not implemented
as 'class2 %in% is(object)'?

Thanks,
H.

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
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P.O. Box 19024
Seattle, WA 98109-1024

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