[R] How to modify object's code living in some environment?
murdoch@dunc@n @end|ng |rom gm@||@com
Mon Dec 27 18:28:11 CET 2021
On 27/12/2021 8:25 a.m., Duncan Murdoch wrote:
> On 27/12/2021 8:06 a.m., Grzegorz Smoliński wrote:
>> I know it is possible to find the environment in which some object
>> lives using the 'environment()' function and the name of this object,
>> but how to modify code of this object after this? Below is MRE:
> You are misunderstanding the relation between environments and
> functions. However, your understanding is also being messed up by a bug
> in R, so it's not entirely your fault.
Actually this isn't a bug in R, it is working as documented. For a
detailed explanation, see the response to my bug report here:
For a quick idea: "complex assignments" are assignments where there is
a complex expression on the left hand side, e.g.
environment(test)$test <- ...
The way these are documented to work (in the R Language Definition
manual) makes intuitive sense when you are working with regular R
objects, but environments are "mutable" objects: assigning them to a
new name doesn't make a new copy, just a new reference. That causes the
definition of the complex assignment above to work in an unintuitive way.
Conclusion: you should avoid using calls like environment(f) on the
left hand side of assignments, especially as part of a larger
expression. Break up the statement into steps like I did below:
> e <- environment(test)
> e$test <- eval(parse(text = "function() 2"))
The same advice would apply to a function that returned an R6 object or
a mutable object from the methods package (which are really environments
in disguise), as well as some other exotic objects.
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