[BUGZILLA #17496] methods::sealClass() does not work without specifying the 'where' argument

[MichaelChirico]

Created attachment 2383 [details]
A patch for sealClass() generated as described in https://www.r-project.org/bugs.html.

Function sealClass() cannot be used without specifying the 'where' argument. This issue exists in R versions 2.15.1 through 3.5.0.

Here is an example of the bug in question:

setClass("foo", slots=c(name="character", age="integer"))
isSealedClass("foo")

[1] FALSE

sealClass("foo")

Error in list2env(list(), NULL, ) :
names(x) must be a character vector of the same length as x

isSealedClass("foo")

[1] FALSE

sealClass("foo", where=.GlobalEnv)
isSealedClass("foo")

[1] TRUE

This error occurs because sealClass() includes the following line:
if (missing(where)) where <- findClass(Class, unique = "sealing the class", where = where)

Because findClass() always returns a list (even if 'unique' contains a character string indicating that a unique location for the class is expected), this statement assigns a list of length 1, containing a single environment, to the variable 'where'.

This results in an error being thrown in the subsequent call to assignClassDef(), which expects the 'where' argument to contain an environment, rather than a list of environments:
assignClassDef(Class, classDef, where)

For this reason, the abovementioned line in sealClass() should instead read:
if (missing(where)) where <- findClass(Class, unique = "sealing the class", where = where)[[1]]

A patch for this bug is attached. Thanks very much for your assistance in this matter.

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METADATA

• Bug author - Adam Gower
• Creation time - 2018-11-02 14:03:13 UTC
• Bugzilla link
• Status - ASSIGNED
• Alias - None
• Component - S4methods
• Version - R 3.5.0
• Hardware - All All
• Importance - P5 normal
• Assignee - Michael Lawrence
• URL -
• Modification time - 2018-11-02 16:00 UTC

[MichaelChirico]

Thanks, will commit.

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METADATA

• Comment author - Michael Lawrence
• Timestamp - 2018-11-02 16:00:45 UTC

[github-actions]

NA

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METADATA

• Comment author - Sebastian Meyer
• Timestamp - 2020-08-06 15:47:51 UTC

[github-actions]

NA

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METADATA

• Comment author - elin.waring
• Timestamp - 2020-09-21 11:18:46 UTC