pub fn pop(&mut self) -> Option<char> {
        if self.older.is_empty(){
            if self.younger.is_empty{
                return None;
            }

            use std::mem::swap;
            swap(&mut self.older, &mut self.younger);
            self.older.reserve();
        }
        self.older.pop();
    }
//pop a character off the front of a queue, 
//Return Some(c) if there was a character to pop
//or None if the queue was empty
pop a character off the front of a queue,
Return Some(c) if there was a character to pop
or None if the queue was empty
pop a character off the front of a queue Return Some ( c ) if there was a character to pop or None if the queue was empty
pub fn pop(&mut self) -> Option<char> {
        if self.older.is_empty(){
            if self.younger.is_empty{
                return None;
            }
            use std::mem::swap;
            swap(&mut self.older, &mut self.younger);
            self.older.reserve();
        }
        self.older.pop();
    }
pub fn pop ( & mut self ) -> Option < char > { if self . older . is_empty ( ) { if self . younger . is_empty { return None ; } use std :: mem :: swap ; swap ( & mut self . older , & mut self . younger ) ; self . older . reserve ( ) ; } self . older . pop ( ) ; }
pop a character off the front of a queue,
Return Some(c) if there was a character to pop
or None if the queue was empty
pop a character off the front of a queue Return Some ( c ) if there was a character to pop or None if the queue was empty
&mut self
&mut self