pub fn is_nothing(&self) -> bool {
        if let SwChangeState::Nothing = self {
            true
        }else{
            false
        }
    }
/// checks if self is `Nothing` variant
checks if self is `Nothing` variant
checks if self is ` Nothing ` variant
pub fn is_nothing(&self) -> bool {
        if let SwChangeState::Nothing = self {
            true
        }else{
            false
        }
    }
pub fn is_nothing ( & self ) -> bool { if let SwChangeState :: Nothing = self { true } else { false } }
checks if self is `Nothing` variant
checks if self is ` Nothing ` variant
&self
&self