Struct Nothing 

pub struct Nothing;

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<(), Error>

Formats the value using the given formatter.

impl Eq for Nothing

Available on crate feature extra-traits only.

impl Hash for Nothing

Available on crate feature extra-traits only.

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

where H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Parse for Nothing

fn parse(_input: &ParseBuffer<'_>) -> Result<Nothing, Error>

impl PartialEq for Nothing

Available on crate feature extra-traits only.

fn eq(&self, _other: &Nothing) -> bool

Equality operator ==.

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

Inequality operator !=.