Is there any way to express to the borrow checker that a pair of FnMut closures will never be called at the same time, allowing both to mutably capture by reference the same value(s)?
I tried attaching the same lifetime to both of them (+ 'a) but that didn't work.
#(FnMut, FnMut)
round sigil
distant plover
No, it is not possible. However:
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I had exactly the same problem and just yesterday realized that I can combine them into one closure with another argument telling it which of the two things to do (in my case, a boolean, but an enum would also work and allow it to have different fields for the two cases).
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Before then, I was using a
RefCellwrapped around the mutable reference they both wanted to use. -
If they have very different signatures then you can make both functions be methods in a trait, instead; this means you have to replace the closure with a
struct+impl, though.
Of these, only option 2 is possible if you don't control the code calling the functions.