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: Display>(self, message: T) -> Error

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.

Methods from Deref<Target = Cursor<'c>>

pub fn eof(self) -> bool

Checks whether the cursor is currently pointing at the end of its valid scope.

pub fn ident(self) -> Option<(Ident, Cursor<'a>)>

If the cursor is pointing at a Ident, returns it along with a cursor pointing at the next TokenTree.

pub fn punct(self) -> Option<(Punct, Cursor<'a>)>

If the cursor is pointing at a Punct, returns it along with a cursor pointing at the next TokenTree.

pub fn literal(self) -> Option<(Literal, Cursor<'a>)>

If the cursor is pointing at a Literal, return it along with a cursor pointing at the next TokenTree.

pub fn lifetime(self) -> Option<(Lifetime, Cursor<'a>)>

If the cursor is pointing at a Lifetime, returns it along with a cursor pointing at the next TokenTree.

pub fn group( self, delim: Delimiter, ) -> Option<(Cursor<'a>, DelimSpan, Cursor<'a>)>

If the cursor is pointing at a Group with the given delimiter, returns a cursor into that group and one pointing to the next TokenTree.

pub fn any_group(self) -> Option<(Cursor<'a>, Delimiter, DelimSpan, Cursor<'a>)>

If the cursor is pointing at a Group, returns a cursor into the group and one pointing to the next TokenTree.

pub fn token_stream(self) -> TokenStream

Copies all remaining tokens visible from this cursor into a TokenStream.

pub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)>

If the cursor is pointing at a TokenTree, returns it along with a cursor pointing at the next TokenTree.

Returns None if the cursor has reached the end of its stream.

This method does not treat None-delimited groups as transparent, and will return a Group(None, ..) if the cursor is looking at one.

pub fn span(self) -> Span

Returns the Span of the current token, or Span::call_site() if this cursor points to eof.

pub fn prev_span(self) -> Span

Returns the Span of the token immediately prior to the position of this cursor, or of the current token if there is no previous one.

Trait Implementations

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

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

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

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

type Target = Cursor<'c>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.