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 Clone for Nothing

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Parse for Nothing

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

impl ToTokens for Nothing

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

Write self to the given TokenStream.

fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object.

fn into_token_stream(self) -> TokenStream

where Self: Sized,

Convert self directly into a TokenStream object.

impl Copy for Nothing