[Rd] Discrepancy between is.list() and is(x, "list")

Hadley Wickham h@w|ckh@m @end|ng |rom gm@||@com
Wed Mar 27 12:38:12 CET 2019

I would recommend reading https://adv-r.hadley.nz/base-types.html and
https://adv-r.hadley.nz/s3.html. Understanding the distinction between
base types and S3 classes is very important to make this sort of
question precise, and in my experience, you'll find R easier to
understand if you carefully distinguish between them. (And hence you
shouldn't expect is.x(), inherits(, "x") and is(, "x") to always
return the same results)

Also note that many of is.*() functions are not testing for types or
classes, but instead often have more complex semantics. For example,
is.vector() tests for objects with an underlying base vector type that
have no attributes (apart from names). is.numeric() tests for objects
with base type integer or double, and that have the same algebraic
properties as numbers.


On Mon, Mar 25, 2019 at 10:28 PM Abs Spurdle <spurdle.a using gmail.com> wrote:
> > I have noticed a discrepancy between is.list() and is(x, “list”)
> There's a similar problem with inherits().
> On R 3.5.3:
> > f = function () 1
> > class (f) = "f"
> > is.function (f)
> [1] TRUE
> > inherits (f, "function")
> [1] FALSE
> I didn't check what happens with:
> > class (f) = c ("f", "function")
> However, they should have the same result, regardless.
> > Is this discrepancy intentional?
> I hope not.
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