fn next_token(&mut self) -> TokenAndSpan {
        let ret_val = TokenAndSpan {
            tok: replace(&mut self.peek_tok, token::Underscore),
            sp: self.peek_span,
        };
        self.advance_token();
        ret_val
    }
/// Return the next token. EFFECT: advances the string_reader.
Return the next token. EFFECT: advances the string_reader.
Return the next token . EFFECT : advances the string_reader .
fn next_token(&mut self) -> TokenAndSpan {
        let ret_val = TokenAndSpan {
            tok: replace(&mut self.peek_tok, token::Underscore),
            sp: self.peek_span,
        };
        self.advance_token();
        ret_val
    }
fn next_token ( & mut self ) -> TokenAndSpan { let ret_val = TokenAndSpan { tok : replace ( & mut self . peek_tok , token :: Underscore ) , sp : self . peek_span , } ; self . advance_token ( ) ; ret_val }
Return the next token.
Return the next token .
&mut self