[Rd] identical(..., ignore.environment=TRUE)

[Duncan Murdoch]

On 12/10/2015 9:51 AM, Ben Bolker wrote:
> Duncan Murdoch <murdoch.duncan <at> gmail.com> writes:
> 
> BB>
>>>> It seems odd/inconvenient to me that the "ignore.environment" argument
>>>> of identical() only applies to closures (which I read as 'functions' --
>>>> someone can enlighten me about the technical differences between
>>>> functions and closures if they like -- see below for consequences of my
>>>> confusion).  This is certainly not a bug, it's clearly documented, but
>>>> it seems like a design flaw.  It would certainly be convenient to be
>>>> able to ignore differences in environments when comparing complex
>>>> objects with lots of deeply nested formula and terms objects with
>>>> environments ...
>>>>
>>>>    Can anyone suggest a reason for this design?
>>>>
> 
>   [snip]
> 
>>>> Actually, maybe I don't understand how this is supposed to work since I
>>>> thought this would be TRUE:
>>>>
>>>>> f1 <- function() {}
>>>>> f2 <- function() {}
>>>>> environment(f1) <- new.env()
>>>>> environment(f2) <- new.env()
>>>>> identical(f1,f2,ignore.environment=TRUE)   ## FALSE
>>>
>>> Those two functions likely have different srcref attributes.  If you
>>> created f2 using f2 <- f1, you'd get your expected result.
>>>
> 
> [snip]
> 
>  Thanks for the clarification about closures vs. functions.
> 
> [snip]
> 
> You're right that the srcref attributes are different; although their
> bodies are the same, they have their own environments that differ.
> For me, this makes the intended use of ignore.environment= even more
> puzzling; given that environments are not ignored recursively (that's
> not exactly what I mean -- I mean ignoring all environments of components
> of an object), I have trouble understanding the use case for
> ignore.environnment ...  maybe it was developed before srcrefs 
> existed?  

I think it simply means "ignore.environment.of.closures", as the
description says, but that's too long to be a convenient arg name.

Closures have three parts:  the formals, the body and the environment.
(Actually, 4 parts:  like almost all R objects, they may also have
attributes.)

That arg just says to ignore the environment part when comparing
closures.  It doesn't say to ignore environments in general.

> 
> In the R code base it's used in checkConflicts (to see if a function
> is re-exported) and in getAnywhere ...
> 

I'd say those uses are slightly bogus.  You should generally remember
that closures have 3 (or 4) parts, and not go around comparing only two
(or 3) of them.

Duncan Murdoch