[Rd] .Call ref card

[Simon Urbanek]

On Mar 27, 2012, at 12:03 PM, Terry Therneau wrote:

> On 03/23/2012 10:58 AM, Simon Urbanek wrote:
>> This is my shot at a cheat sheet.
>> comments are welcome.
>> 
>> Simon
>> 
>> 
> I was looking through the cheat sheet.  It's nice.  There are a few things in it that I can't find in the documentation though.  Where would one find a description?  (I can guess, but that may be dangerous).
> 
> mkNamed

It is a shorthand for using allocVector and then setting names (which can be tedious). It's a simple way to create a result list/object (a very common thing to do):

    SEXP res = PROTECT(mkNamed(VECSXP, (const char*[]) { "foo", "bar", ""}));
    // fill res with SET_VECTOR_ELT(res, ..) 
    setAttrib(res, R_ClassSymbol, mkString("myClass"));
    UNPROTECT(1);
    return res;

Note that the sentinel is "" (not not NULL as commonly used in other APIs). Also you don't specify the length because it is determined from the names.


> R_Naint   (I don't see quite how this differs from using NA_INTEGER to set a result)

It doesn't really -- NA_INTEGER is defined to be R_NaInt. In theory NA_INTEGER being a macro could be a constant instead -- maybe for efficiency -- but currently it's not.


> R_PreserveObject, R_ReleaseObject   (Advantages/disadvantages wrt PRESERVE?)
> 

I guess you mean wrt PROTECT? Preserve/Release is used for objects that you want to be globally preserved - i.e. they will survive exit from the function. In contrast, the protection stack is popped when you exit the function (both by error or success).

Cheers,
Simon