Struct syn::parse::Nothing

pub struct Nothing;

Available on crate feature parsing only.

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

impl Debug for Nothing

Available on crate feature extra-traits only.

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

Formats the value using the given formatter.

impl Hash for Nothing

Available on crate feature extra-traits only.

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

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl Parse for Nothing

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

impl PartialEq<Nothing> for Nothing

Available on crate feature extra-traits only.

fn eq(&self, _other: &Self) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl Eq for Nothing

Available on crate feature extra-traits only.