Message-ID: <4AF3310A.4020702@acm.org>
Date: 2009-11-05T20:09:46Z
From: Tony Plate
Subject: Active bindings in attached environments
In-Reply-To: <a8cee7640911051137v62f57aefm768451e0a9c3b486@mail.gmail.com>
An explanation of this would be nice in ?makeActiveBinding, e.g.,
NOTE:
When an environment is attach()'ed to the search path, any active
bindings in it are not preserved as active bindings. This happens
because attach() actually adds a new environment to the search path, and
copies objects into it. Thus, active bindings are evaluated and their
values copied into the attached environment.
(Is this explanation correct?)
-- Tony Plate
(PS: Thunderbird wants to spell-correct "makeActiveBinding" to
"vindictivenesses", which seems an amusingly appropriate allusion to the
nature of this "gotcha" :-)
Jeffrey Horner wrote:
> On Thu, Nov 5, 2009 at 9:53 AM, Jeffrey Horner <jeffrey.horner at gmail.com> wrote:
>
>> Hi,
>>
>> Is this expected behavior for active bindings in attached
>> environments, or is this a bug:
>>
>>
>>> e <- new.env()
>>> makeActiveBinding('x',function() 'foo',e)
>>> ls(e)
>>>
>> [1] "x"
>>
>>> attach(e)
>>> search()
>>>
>> [1] ".GlobalEnv" "e" "package:graphics"
>> [4] "package:grDevices" "package:datasets" "package:utils"
>> [7] "package:methods" "Autoloads" "package:base"
>>
>>> x
>>>
>> function() 'foo'
>>
>> Should this print 'foo' ? The following works as I would expect:
>>
>>
>>> with(e,x)
>>>
>> [1] "foo"
>>
>> but this doesn't:
>>
>>
>>> f <- function() x
>>> f()
>>>
>> function() 'foo'
>>
>> However, changing the environment of f does:
>>
>>
>>> environment(f) <- e
>>> f()
>>>
>> [1] "foo"
>>
>
> Actually, it is my understanding of attach() which is the bug. The
> attach documentation clearly states that a copy of the object is
> attached, not the object itself.
>
> Thanks,
>
> Jeff
> --
> http://biostat.mc.vanderbilt.edu/JeffreyHorner
>
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