Hi,
>I have run into an issue while developing an R package. Specifically, my issue
>relates to what happens when I define an S3 length
>method for my class. Here is my basic setup:
># Here is the structure of myClass
># uses an externalptr to operate on file using some C functions list(file =
>"my/file/location", handle = <externalptr>)
># this function gets an S3Method() in NAMESPACE length.myClass <- function(x) {
> .Call("get_class_length",myPkg)
>}
>As you can see, myClass is just a list of two pieces of information about the
>particular object. Without a defined length method, length(myClass) would be
>2. However, I defined a length method to give me the information about the
>amount of binary messages contained in the file the object points to. In one
>of my test files there are 82 messages and length(myObject) correctly returns
>82. What I ran into is that I was crashing RStudio when rebuilding my package
>with an object of myClass in my environment. Only
> removing my S3 length method caused the crash to not occur. After looking for
> memory leaks and other errors I finally noticed that > the str() on the
> object of myClass looked odd. It returned something like this:
> List of 82
> $ file : chr "my/file/location"
> $ handle:<externalptr>
>$ NA:
>Error in object[[i]] : subscript out of bounds
You could define methods for indexing ("[" and "[[") for objects from your
class.
Since you have not defined special subsetting methods for your class, R uses a
default one, but honours your length(), hence the mess.
Regards,
Georgi Boshnkaov
-----Original Message-----
From: R-package-devel [mailto:r-package-devel-boun...@r-project.org] On Behalf
Of Nathan Wendt
Sent: 30 January 2016 19:25
To: r-package-devel@r-project.org
Subject: [R-pkg-devel] S3 length method behavior
Hello,
I have run into an issue while developing an R package. Specifically, my issue
relates to what happens when I define an S3 length method for my class. Here is
my basic setup:
# Here is the structure of myClass
# uses an externalptr to operate on file using some C functions list(file =
"my/file/location", handle = <externalptr>)
# this function gets an S3Method() in NAMESPACE length.myClass <- function(x) {
.Call("get_class_length",myPkg)
}
As you can see, myClass is just a list of two pieces of information about the
particular object. Without a defined length method, length(myClass) would be 2.
However, I defined a length method to give me the information about the amount
of binary messages contained in the file the object points to. In one of my
test files there are 82 messages and length(myObject) correctly returns 82.
What I ran into is that I was crashing RStudio when rebuilding my package with
an object of myClass in my environment. Only removing my S3 length method
caused the crash to not occur. After looking for memory leaks and other errors
I finally noticed that the str() on the object of myClass looked odd. It
returned something like this:
List of 82
$ file : chr "my/file/location"
$ handle:<externalptr>
$ NA:
Error in object[[i]] : subscript out of bounds
It seems that when I define an S3 method for length that somehow the object of
myClass then gets restructured to have the length returned by the function.
There are 82 messages in the file, but myClass objects should only have two
elements. My best guess here is that the RStudio crash was happening because
the object was misrepresented internally. Of course, I cannot be sure. None of
my tests pointed to anything useful.
My questions are, then, whether this behavior makes sense and what to do about
it. If I define my own str() method, will that fix it? I think I am just
misunderstanding what is going on with the methods I have defined.
Hopefully, someone can offer some clarity.
Thanks,
[[alternative HTML version deleted]]
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