[R] a weird question about gdata:::

[Gabor Grothendieck]

On Sun, Dec 4, 2011 at 6:57 PM, Rolf Turner <rolf.turner at xtra.co.nz> wrote:
>
> See end of message.
>
>
> On 05/12/11 10:19, Erin Hodgess wrote:
>>
>> Dear R People:
>>
>> If I put in:
>>
>>> findPerl
>>
>> Error: object 'findPerl' not found
>>
>>
>> But if I use:
>>
>>> gdata:::findPerl
>>
>> function (perl, verbose = "FALSE")
>> {
>>     errorMsg<- "perl executable not found. Use perl= argument to
>> specify the correct path."
>>     if (missing(perl)) {
>>         perl = "perl"
>>     }
>>     perl = Sys.which(perl)
>>     if (perl == "" || perl == "perl")
>>         stop(errorMsg)
>>     if (.Platform$OS == "windows") {
>>         if (length(grep("rtools", tolower(perl)))>  0) {
>>             perl.ftype<- shell("ftype perl", intern = TRUE)
>>             if (length(grep("^perl=", perl.ftype))>  0) {
>>                 perl<- sub("^perl=\"([^\"]*)\".*", "\\1", perl.ftype)
>>             }
>>         }
>>     }
>>     if (verbose)
>>         cat("Using perl at", perl, "\n")
>>     perl
>> }
>> <environment: namespace:gdata>
>> Why does one work but not the other, please?
>
>
> Because "findPerl" is ``not exported'' from the gdata namespace.
>
> Uhhh, what does that mean?  I have a vague idea, but I'm not sufficiently
> confident/competent to elaborate.  You'll just have to read up on
> namespaces.
> I'm *sure* namespaces are really a Good Thing, but they sure do add to the
> mysteries of R usage.
>

The idea is to divide objects into those that are there for the user
to access (exported objects) and those that are internal objects that
only the package itself uses (everything else).   findPerl is there
only so that read.xls and other routines that depend on perl scripts
can use it internally to find perl.  It was not intended that users
access it so its better hidden from view.

-- 
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