Struct StepCursor

pub struct StepCursor<'c, 'a> { /* private fields */ }

Cursor state associated with speculative parsing.

This type is the input of the closure provided to ParseStream::step.

Example

use proc_macro2::TokenTree;
use syn::Result;
use syn::parse::ParseStream;

// This function advances the stream past the next occurrence of `@`. If
// no `@` is present in the stream, the stream position is unchanged and
// an error is returned.
fn skip_past_next_at(input: ParseStream) -> Result<()> {
    input.step(|cursor| {
        let mut rest = *cursor;
        while let Some((tt, next)) = rest.token_tree() {
            match &tt {
                TokenTree::Punct(punct) if punct.as_char() == '@' => {
                    return Ok(((), next));
                }
                _ => rest = next,
            }
        }
        Err(cursor.error("no `@` was found after this point"))
    })
}

Implementations

impl<'c, 'a> StepCursor<'c, 'a>

pub fn error<T>(self, message: T) -> Error

where T: Display,

Triggers an error at the current position of the parse stream.

The ParseStream::step invocation will return this same error without advancing the stream state.

Trait Implementations

impl<'c, 'a> Clone for StepCursor<'c, 'a>

fn clone(&self) -> StepCursor<'c, 'a>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'c, 'a> Deref for StepCursor<'c, 'a>

type Target = Cursor<'c>

The resulting type after dereferencing.

fn deref(&self) -> &<StepCursor<'c, 'a> as Deref>::Target

Dereferences the value.

impl<'c, 'a> Copy for StepCursor<'c, 'a>