## Spacing

# Enum Spacing

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    pub enum Spacing {
        Alone,
        Joint,
        JointHidden,
    }

Expand description

Indicates whether a token can join with the following token to form a compound token. Used for conversions to `proc_macro::Spacing`. Also used to guide pretty-printing, which is where the `JointHidden` value (which isn’t part of `proc_macro::Spacing`) comes in useful.

## Variants§

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### Alone

The token cannot join with the following token to form a compound token.

In token streams parsed from source code, the compiler will use `Alone` for any token immediately followed by whitespace, a non-doc comment, or EOF.

When constructing token streams within the compiler, use this for each token that (a) should be pretty-printed with a space after it, or (b) is the last token in the stream. (In the latter case the choice of spacing doesn’t matter because it is never used for the last token. We arbitrarily use `Alone`.)

Converts to `proc_macro::Spacing::Alone`, and `proc_macro::Spacing::Alone` converts back to this.

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### Joint

The token can join with the following token to form a compound token.

In token streams parsed from source code, the compiler will use `Joint` for any token immediately followed by punctuation (as determined by `Token::is_punct`).

When constructing token streams within the compiler, use this for each token that (a) should be pretty-printed without a space after it, and (b) is followed by a punctuation token.

Converts to `proc_macro::Spacing::Joint`, and `proc_macro::Spacing::Joint` converts back to this.

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### JointHidden

The token can join with the following token to form a compound token, but this will not be visible at the proc macro level. (This is what the `Hidden` means; see below.)

In token streams parsed from source code, the compiler will use `JointHidden` for any token immediately followed by anything not covered by the `Alone` and `Joint` cases: an identifier, lifetime, literal, delimiter, doc comment.

When constructing token streams, use this for each token that (a) should be pretty-printed without a space after it, and (b) is followed by a non-punctuation token.

Converts to `proc_macro::Spacing::Alone`, but `proc_macro::Spacing::Alone` converts back to `token::Spacing::Alone`. Because of that, pretty-printing of `TokenStream`s produced by proc macros is unavoidably uglier (with more whitespace between tokens) than pretty-printing of `TokenStream`’s produced by other means (i.e. parsed source code, internally constructed token streams, and token streams produced by declarative macros).

## Trait Implementations§

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### impl Clone for Spacing

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#### fn clone(&self) -> Spacing

Returns a duplicate of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for Spacing

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl<__D: SpanDecoder> Decodable<__D> for Spacing

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#### fn decode(__decoder: &mut __D) -> Self

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### impl<__E: SpanEncoder> Encodable<__E> for Spacing

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#### fn encode(&self, __encoder: &mut __E)

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### impl<__CTX> HashStable<__CTX> for Spacing
where __CTX: HashStableContext,

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#### fn hash_stable(&self, __hcx: &mut __CTX, __hasher: &mut StableHasher)

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### impl PartialEq for Spacing

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#### fn eq(&self, other: &Spacing) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl Copy for Spacing

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### impl StructuralPartialEq for Spacing

## Auto Trait Implementations§

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### impl DynSend for Spacing

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### impl DynSync for Spacing

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### impl Freeze for Spacing

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### impl RefUnwindSafe for Spacing

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### impl Send for Spacing

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### impl Sync for Spacing

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### impl Unpin for Spacing

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### impl UnwindSafe for Spacing

## Blanket Implementations§

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### impl<T> Aligned for T

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#### const ALIGN: Alignment

Alignment of `Self`.
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### impl<T> Any for T
where 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 T
where 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 T
where 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> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. Read more
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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> Instrument for T

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#### fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
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#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
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### impl<T, U> Into<U> for T
where 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> IntoEither for T

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#### fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left` is `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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#### fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left(&self)` returns `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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### impl<T> MutVisitorResult for T

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#### type Result = ()

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### impl<T> Pointable for T

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#### const ALIGN: usize

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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### impl<T> Same for T

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#### type Output = T

Should always be `Self`
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### impl<T> ToOwned for T
where 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 T
where 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 T
where 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<T> WithSubscriber for T

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#### fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 1 byte

Size for each variant:

- `Alone`: 0 bytes
- `Joint`: 0 bytes
- `JointHidden`: 0 bytes