pub enum MutBorrowKind {
    Default,
    TwoPhaseBorrow,
    ClosureCapture,
}

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Default

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TwoPhaseBorrow

This borrow arose from method-call auto-ref. (i.e., adjustment::Adjust::Borrow)

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ClosureCapture

Data must be immutable but not aliasable. This kind of borrow cannot currently be expressed by the user and is used only in implicit closure bindings. It is needed when the closure is borrowing or mutating a mutable referent, e.g.:

let mut z = 3;
let x: &mut isize = &mut z;
let y = || *x += 5;

If we were to try to translate this closure into a more explicit form, we’d encounter an error with the code as written:

struct Env<'a> { x: &'a &'a mut isize }
let mut z = 3;
let x: &mut isize = &mut z;
let y = (&mut Env { x: &x }, fn_ptr);  // Closure is pair of env and fn
fn fn_ptr(env: &mut Env) { **env.x += 5; }

This is then illegal because you cannot mutate an &mut found in an aliasable location. To solve, you’d have to translate with an &mut borrow:

struct Env<'a> { x: &'a mut &'a mut isize }
let mut z = 3;
let x: &mut isize = &mut z;
let y = (&mut Env { x: &mut x }, fn_ptr); // changed from &x to &mut x
fn fn_ptr(env: &mut Env) { **env.x += 5; }

Now the assignment to **env.x is legal, but creating a mutable pointer to x is not because x is not mutable. We could fix this by declaring x as let mut x. This is ok in user code, if awkward, but extra weird for closures, since the borrow is hidden.

So we introduce a ClosureCapture borrow – user will not have to mark the variable containing the mutable reference as mut, as they didn’t ever intend to mutate the mutable reference itself. We still mutable capture it in order to mutate the pointed value through it (but not mutating the reference itself).

This solves the problem. For simplicity, we don’t give users the way to express this borrow, it’s just used when translating closures.

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> CallHasher for Twhere T: Hash + ?Sized,

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default fn get_hash<H, B>(value: &H, build_hasher: &B) -> u64where H: Hash + ?Sized, B: BuildHasher,

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impl<Q, K> Comparable<K> for Qwhere Q: Ord + ?Sized, K: Borrow<Q> + ?Sized,

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fn compare(&self, key: &K) -> Ordering

Compare self to key and return their ordering.
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impl<Q, K> Equivalent<K> for Qwhere Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Qwhere Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<N> NodeTrait for Nwhere N: Copy + Ord + Hash,