fn next_char(&mut self) -> Result<char> {
        let ch = self.peek_char()?;
        self.input = &self.input[ch.len_utf8()..];
        Ok(ch)
    }
/// Consume the first character in the input.
Consume the first character in the input.
Consume the first character in the input .
fn next_char(&mut self) -> Result<char> {
        let ch = self.peek_char()?;
        self.input = &self.input[ch.len_utf8()..];
        Ok(ch)
    }
fn next_char ( & mut self ) -> Result < char > { let ch = self . peek_char ( ) ? ; self . input = & self . input [ ch . len_utf8 ( ) .. ] ; Ok ( ch ) }
Consume the first character in the input.
Consume the first character in the input .
&mut self
&mut self