# iter.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro-hack-0.5.19/src/iter.rs`.
Keywords: rust, rustlang, rust-lang

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    use proc_macro::{token_stream, Delimiter, TokenStream, TokenTree};

    pub type Iter<'a> = &'a mut IterImpl;

    pub struct IterImpl {
        stack: Vec<token_stream::IntoIter>,
        peeked: Option<TokenTree>,
    }

    pub fn new(tokens: TokenStream) -> IterImpl {
        IterImpl {
            stack: vec![tokens.into_iter()],
            peeked: None,
        }
    }

    impl IterImpl {
        pub fn peek(&mut self) -> Option<&TokenTree> {
            self.peeked = self.next();
            self.peeked.as_ref()
        }
    }

    impl Iterator for IterImpl {
        type Item = TokenTree;

        fn next(&mut self) -> Option<Self::Item> {
            if let Some(tt) = self.peeked.take() {
                return Some(tt);
            }
            loop {
                let top = self.stack.last_mut()?;
                match top.next() {
                    None => drop(self.stack.pop()),
                    Some(TokenTree::Group(ref group)) if group.delimiter() == Delimiter::None => {
                        self.stack.push(group.stream().into_iter());
                    }
                    Some(tt) => return Some(tt),
                }
            }
        }
    }