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[R-pkg-devel] double colon

4 messages · Berry Boessenkool, Uwe Ligges, Duncan Murdoch

Original
Berry Boessenkool
# 
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? 
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?
If Answer1==YES:
Should I also refer to other functions within my own package through   myPackage::otherFunction?
Should I do that for base packages like graphics, stats, utils, grDevices? (we have to declare them in the NAMESPACE imports, after all)
What's a fast and easy way to find all the instances of 'external' function usage?

I guess there must be discussions and guidelines about this, so some pointers instead of answers would be fine as well.
Thanks ahead,
Berry
Uwe Ligges
#
On 29.01.2016 15:21, Berry Boessenkool wrote:
No, *if* you import anyway (see below).
Yes.
Yes, *if* you only suggest the package and do not import from the 
namespace unconditionally, you should do that.


Best,
Uwe Ligges
Duncan Murdoch
#
On 29/01/2016 10:56 AM, Uwe Ligges wrote:
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
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).
Berry Boessenkool
# 
Thanks for your reply, Uwe.
The guy yesterday very strongly suggested it for user readability, but I wanted to get more opinions before doing so much work. (No offense, Steven).

I'm not sure whether we talk about the same thing considering functions *within* the package.
Say I have 'MyPackage' with 'fun_a' and also 'fun_b', which inside calls 'fun_a'. (Both exported)
That wouldn't be in imports or suggests, right?

Now image by unfortunate history there is 'AnotherPackage' that also has (its own and different) 'fun_a'.
Is far as I remember, 'fun_b' will still call 'fun_a' from 'MyPackage'.
I can't find back where I read that, though.
For user readability and to be on the safe side, in the future I'll write 'MyPackage::fun_a'.
(Of course, if I'm aware, I'll avoid same-name functions altogether).

kind regards,
Berry