Struct syn::parse::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

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

This method 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§

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> 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.