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The returned pointer can now outlive the guard a= nd >> >> > mutation through that pointer is trivial. >> >> >> >> I don't think this is unsound. If we returned a reference instead, it >> >> would be, but we are returning a raw pointer. Dereferencing the point= er >> >> is unsafe and requires proper safety comments. >> > >> > You may be right, strictly speaking, but it is most definitely a >> > footgun. This is a special pointer that requires more careful handling >> > than other raw pointers. >> >> I would disagree. Dereferencing any raw pointer requires the same >> checks, and knowing this one is valid and satisfies lifetime >> requirements is no different than others. >> >> It is also a private method that is only used in this particular impl >> block. >> >> At any rate, I'm fine with dropping the change. The reason I did it was >> because I had to double take when I read the previous code. I think the >> original code is has some unnecessary complexity with the closure. > > Simplification is always welcome. The current shape of this code was > guided by the desire to avoid the footgun we're discussing here. Using a closure isn't any better than just returning a raw pointer. If you = want a pointer you can just have a identity closure and there's nothing preventi= ng you from doing that. Even with `T::borrow` inside the closure this isn't providing any security = as the code would still compile if you change `'_` in the return signature int= o `'static`. The only defence here is really the `unsafe` and safety comment. I would prefer to not have closure in this case. Best, Gary