Struct Lookahead1

pub(crate) struct Lookahead1<'a, 'cx> {
    expected: Vec<&'static str>,
    cx: &'a mut ParseCtxt<'cx>,
}

Support for checking the next token in a stream to decide how to parse.

An important advantage of using this struct over ParseCtxt::peek is that here we automatically construct an appropriate error message based on the token alternatives that get peeked.

Use ParseCtxt::lookahead1 to construct this object.

Fields

expected: Vec<&'static str>

List of “expected” tokens that have been peeked by this struct

cx: &'a mut ParseCtxt<'cx>

Implementations

impl<'a, 'cx> Lookahead1<'a, 'cx>

fn new(cx: &'a mut ParseCtxt<'cx>) -> Self

pub(crate) fn peek<T: Peek>(&mut self, t: T) -> bool

Like ParseCtxt::lookahead1 but it records the expected token to construct an error in case parsing can’t proceed. If this method returns true, this Lookahead1 object should be discarded.

pub(crate) fn advance_if<T: Peek>(&mut self, t: T) -> bool

Like ParseCtxt::advance_if but it records the expected token to construct an error in case parsing can’t proceed. If this method returns true, this Lookahead1 object should be discarded.

pub(crate) fn into_error(self) -> ParseError

Create an unexpected token error based on the expected tokens that have been peeked with this Lookahead1 object.