[R-pkg-devel] double colon

[Duncan Murdoch]

On 29/01/2016 10:56 AM, Uwe Ligges wrote:
>
> On 29.01.2016 15:21, Berry Boessenkool wrote:
> >
> > Hi,
> > in our Berlin R User Group meeting yesterday we talked about dependencies in package development.
> > One thing that came up is that it's a good practice to explicitly write   package::function   in the code.
> >
> > Is it worth to go through all of my package and enhance the code in all instances?
>
> No, *if* you import anyway (see below).
>
>
> > Or do you think that NAMESPACE sufficiently prevents using a function with the same name from another package than intended and people reading source code should be aware of that anyways?
>
> Yes.

I'd add one caveat here:  if you explicitly import things by name, this 
is definitely true.

If you import everything from another package, then conceivably you 
could end up with problems:  e.g. you import all of package A and all of 
package B.  You want Fn from B, and since A doesn't have a function like 
that, you're fine.  But later if package A adds a function called Fn,  
you might get in trouble and end up using the wrong one.

So use

importFrom(A, something)
importFrom(B, Fn)

rather than

import(A, B)

Duncan Murdoch

>
>
> > If Answer1==YES:
> > Should I also refer to other functions within my own package through   myPackage::otherFunction?
>
> Yes, *if* you only suggest the package and do not import from the
> namespace unconditionally, you should do that.

I think Berry was referring to the case where package Foo has function 
Fn, and was asking whether he should use Foo::Fn within the code of 
package Foo.  The answer to that is no.  Your own locally defined 
functions generally have precedence over ones from other packages 
(unless you mess around with environments; don't do that).