Temporarily move out of borrowed content

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The code above doesn’t work, and understandibly so, moving the value
out of self breaks the integrity of it.

This is not exactly what happens here. For example, same thing with self would work nicely:

impl<T> Foo<T> {
    fn switch(self) {
        self = match self {
            Foo::Bar(val) => Foo::Baz(val),
            Foo::Baz(val) => Foo::Bar(val),
        }
    }
}

Rust is absolutely fine with partial and total moves. The problem here is that you do not own the value you’re trying to move – you only have a mutable borrowed reference. You cannot move out of any reference, including mutable ones.

This is in fact one of the frequently requested features – a special kind of reference which would allow moving out of it. It would allow several kinds of useful patterns. You can find more here and here.

In the meantime for some cases you can use std::mem::replace and std::mem::swap. These functions allow you to “take” a value out of mutable reference, provided you give something in exchange.

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