Maybe I’m misunderstanding, but why is that not possible with a

    Fn(_: T) -> T

▲ iknowstuff 5 days ago | parent | next [-]

It totally is

https://docs.rs/tokio-uring/latest/tokio_uring/fs/struct.Fil...

▲ dwattttt 5 days ago | parent | prev | next [-]

As sibling notes, it is. It's very rarely seen though.

One place you might see something like it is if an API takes ownership, but returns it on error; you see the error side carry the resource you gave it, so you could try again.

▲ IshKebab 5 days ago | parent | prev [-]

How is that different to

  Fn(_: &mut T)

?

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Soft 5 days ago | parent [-]

In the former the caller does not retain access to T until Fn returns.

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andyferris 5 days ago | parent | next [-]

I think I'm lost. If I give a mutable reference to a function... I can't access it (even read it) until it returns, no?

What is different?

	▲	zbentley 4 days ago \| parent [-]
		Let's say a function "foo" calls "fn bar(_: &mut T) -> ()". When passing a mutable reference, the lifetime of the object is largely decided by "foo" (with some caveats). Now, let's say that "foo" instead calls "fn bar(_: T) -> T". When passing the object itself, the lifetime is largely decided/decide-able by "bar".

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IshKebab 5 days ago | parent | prev [-]

That's true of mutable references too though isn't it? In fact lots of people have suggested they should really have been called "exclusive references", since you can actually mutate some objects through non-exclusive references (called "interior mutability" normally).