# Nothing in syn::parse - Rust
An empty syntax tree node that consumes no tokens when parsed.

syn::parse

# Struct Nothing

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    pub struct Nothing;

Expand description

An empty syntax tree node that consumes no tokens when parsed.

This is useful for attribute macros that want to ensure they are not provided any attribute args.

    use proc_macro::TokenStream;
    use syn::parse_macro_input;
    use syn::parse::Nothing;

    #[proc_macro_attribute]
    pub fn my_attr(args: TokenStream, input: TokenStream) -> TokenStream {
        parse_macro_input!(args as Nothing);

        /* ... */
    }

    error: unexpected token
     --> src/main.rs:3:19
      |
    3 | #[my_attr(asdf)]
      |           ^^^^

## Trait Implementations§

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### impl Clone for Nothing

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

Returns a copy 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 Nothing

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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 Hash for Nothing

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#### fn hash<H: Hasher>(&self, _state: &mut H)

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl Parse for Nothing

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#### fn parse(_input: ParseStream<'_>) -> Result<Self>

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### impl PartialEq for Nothing

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#### fn eq(&self, _other: &Self) -> 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 ToTokens for Nothing

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#### fn to_tokens(&self, tokens: &mut TokenStream)

Write `self` to the given `TokenStream`. Read more
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#### fn to_token_stream(&self) -> TokenStream

Convert `self` directly into a `TokenStream` object. Read more
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#### fn into_token_stream(self) -> TokenStream
where Self: Sized,

Convert `self` directly into a `TokenStream` object. Read more
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### impl Copy for Nothing

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### impl Eq for Nothing

## Auto Trait Implementations§

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### impl Freeze for Nothing

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### impl RefUnwindSafe for Nothing

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### impl Send for Nothing

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### impl Sync for Nothing

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### impl Unpin for Nothing

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### impl UnwindSafe for Nothing

## Blanket Implementations§

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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, dst: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dst`. 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, 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> Spanned for T
where T: Spanned + ?Sized,

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#### fn span(&self) -> Span

Returns a `Span` covering the complete contents of this syntax tree node, or `Span::call_site()` if this node is empty.
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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.