R devel - Mar 2016 - formals(x)<- drops attributes including class

Just checking in to see whether it is intended or not that assigning
new formals to a function/closure causes any attributes to be dropped:

EXAMPLE:
> fcn <- structure(function() {}, foo="foo",
class=c("foo"))
> str(fcn)
function ()
 - attr(*, "srcref")=Class 'srcref'  atomic [1:8] 1 18 1 30 18
30 1 1
  .. ..- attr(*, "srcfile")=Classes 'srcfilecopy',
'srcfile' <environment: 0x000
000000c00d128>
 - attr(*, "foo")= chr "foo"
 - attr(*, "class")= chr "foo"
> formals(fcn) <- list(a=1)
> str(fcn)
function (a = 1)
> attributes(fcn)
NULL


TROUBLESHOOTING:
>From the definition of formals()<-, it's quite clear why this
happens:
> `formals<-`
function (fun, envir = environment(fun), value)
{
    bd <- body(fun)
    as.function(c(value, if (is.null(bd) || is.list(bd)) list(bd) else bd),
        envir)
}
<bytecode: 0x000000000b97a848>
<environment: namespace:base>


I'm fine with this, but I just wanted to make sure it's not overlooked.

/Henrik

On 13/03/2016 9:54 AM, Henrik Bengtsson wrote:
> Just checking in to see whether it is intended or not that assigning
> new formals to a function/closure causes any attributes to be dropped:
For srcref, yes.  Changing the formals or body of a function would 
usually make them invalid.

I think it makes a reasonable default behaviour for other attributes as 
well.

Duncan Murdoch
>
> EXAMPLE:
>> fcn <- structure(function() {}, foo="foo",
class=c("foo"))
>> str(fcn)
> function ()
>   - attr(*, "srcref")=Class 'srcref'  atomic [1:8] 1 18 1
30 18 30 1 1
>    .. ..- attr(*, "srcfile")=Classes 'srcfilecopy',
'srcfile' <environment: 0x000
> 000000c00d128>
>   - attr(*, "foo")= chr "foo"
>   - attr(*, "class")= chr "foo"
>
>> formals(fcn) <- list(a=1)
>> str(fcn)
> function (a = 1)
>> attributes(fcn)
> NULL
>
>
> TROUBLESHOOTING:
>>From the definition of formals()<-, it's quite clear why this
happens:
>
>> `formals<-`
> function (fun, envir = environment(fun), value)
> {
>      bd <- body(fun)
>      as.function(c(value, if (is.null(bd) || is.list(bd)) list(bd) else
bd),
>          envir)
> }
> <bytecode: 0x000000000b97a848>
> <environment: namespace:base>
>
>
> I'm fine with this, but I just wanted to make sure it's not
overlooked.
>
> /Henrik
>
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