On 27/12/2021 8:06 a.m., Grzegorz Smoliński wrote:
Hi,
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.
More details below:
test <- function() 1
test() # 1
environment(test)$test <- eval(parse(text = "function() 2"))
First: while it's usually true that function f will be found in
environment(f), these are really separate concepts.
The environment of a function is where it will start looking for
non-local variables. It is initially the environment in which the
function definition is evaluated.
The environment holding a function can be completely different. This
most commonly shows up when you have functions that create other
functions. For example,
factory <- function(x) {
force(x)
function() print(x)
}
f <- factory(3)
f()
which will print 3. Here environment(f) is the evaluation frame of the
call to factory(3), while f is not stored there, it is stored in the
global environment. (If you run ls(environment(f)) you won't see "f"
listed, only "x".)
In your first line "test <- function() 1" you create a function named
test in the global environment whose environment is also the global
environment.
The third line should do what you want, i.e. put the new definition into
the environment of the test function, using the name test, but it
doesn't: I think that's a bug in R. It should be equivalent to
.GlobalEnv$test <- eval(parse(text = "function() 2"))
or
test <- eval(parse(text = "function() 2"))
but as you saw, it's not. They do what you were expecting your third
line to do.
test() # still 1
.GlobalEnv$test <- eval(parse(text = "function() 3"))
test() # 3
The context is I have shiny app which code I would like to modify (add
something) and the only way to refer to this environment I know is to
use 'environment()' (as I see, those functions do not live in
.GlobalEnv), but as you can see above, I can't use it to modify the
code.
You can, as long as you work around the bug in R. Just change that
third line into two statements:
e <- environment(test)
e$test <- eval(parse(text = "function() 2"))
Duncan Murdoch
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