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/// Type for which instances can be partially enumerated.
pub trait PartialEnum: Sized + PartialOrd {
	fn pred(&self) -> Option<Self>;

	fn succ(&self) -> Option<Self>;
}

/// Type for which instances can be entirely enumerated.
pub trait Enum: Sized + PartialOrd {
	fn pred(&self) -> Option<Self>;

	fn succ(&self) -> Option<Self>;
}

impl<T: Enum> PartialEnum for T {
	fn pred(&self) -> Option<Self> {
		self.pred()
	}

	fn succ(&self) -> Option<Self> {
		self.succ()
	}
}

impl Enum for char {
	fn pred(&self) -> Option<Self> {
		match self {
			'\u{0000}' => None,
			'\u{e000}' => Some('\u{d7ff}'),
			_ => Some(unsafe { std::char::from_u32_unchecked(*self as u32 - 1) }),
		}
	}

	fn succ(&self) -> Option<Self> {
		match self {
			'\u{10ffff}' => None,
			'\u{d7ff}' => Some('\u{e000}'),
			_ => Some(unsafe { std::char::from_u32_unchecked(*self as u32 + 1) }),
		}
	}
}

macro_rules! impl_int {
	($($ty:ident),*) => {
		$(
			impl Enum for $ty {
				fn pred(&self) -> Option<Self> {
					self.checked_sub(1)
				}

				fn succ(&self) -> Option<Self> {
					self.checked_add(1)
				}
			}
		)*
	};
}

impl_int!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);

macro_rules! impl_float {
	($($ty:ident),*) => {
		$(
			impl PartialEnum for $ty {
				fn pred(&self) -> Option<Self> {
					None
				}

				fn succ(&self) -> Option<Self> {
					None
				}
			}
		)*
	};
}

impl_float!(f32, f64);