pub fn postfix_increment(&mut self) -> Self {
        let old = *self;
        *self += 1;
        old
    }
/// returns current val and increments it by one after
returns current val and increments it by one after
returns current val and increments it by one after
pub fn postfix_increment(&mut self) -> Self {
        let old = *self;
        *self += 1;
        old
    }
pub fn postfix_increment ( & mut self ) -> Self { let old = * self ; * self += 1 ; old }
returns current val and increments it by one after
returns current val and increments it by one after
&mut self