pub trait Narrow{
	type Output;
	fn narrow(self)->Self::Output;
}
#[derive(Debug)]
pub enum NarrowError{
	Overflow,
	Underflow,
}
pub trait TryNarrow{
	type Output;
	fn try_narrow(self)->Result<Self::Output,NarrowError>;
}
#[cfg(test)]
mod tests {
	use super::*;

	impl TryNarrow for i16{
		type Output=i8;
		fn try_narrow(self)->Result<Self::Output,NarrowError>{
			if self<i8::MIN as i16{
				return Err(NarrowError::Underflow);
			}
			if (i8::MAX as i16)<self{
				return Err(NarrowError::Overflow);
			}
			Ok(self as i8)
		}
	}

	#[test]
	fn test_i16_i8(){
		assert!(matches!(257i16.try_narrow(),Err(NarrowError::Overflow)));
		assert!(matches!(64i16.try_narrow(),Ok(64i8)));
		assert!(matches!((-257i16).try_narrow(),Err(NarrowError::Underflow)));
	}
}