Method pop

publication/code/chapter04/infix_to_postfix.rs:24–28

(&mut self)

    }

    fn pop(&mut self) -> Option<T> {
        if 0 == self.top { return None; }
        self.top -= 1;
        self.data.pop()
    }

    fn peek(&self) -> Option<&T> {
        if 0 == self.top { return None; }