narrow concept

fixed_wide/src/lib.rs

@@ -1,2 +1,3 @@
 pub mod wide;
 pub mod types;
+pub mod narrow;

fixed_wide/src/narrow.rs

@@ -0,0 +1,37 @@
+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)));
+	}
+}

fixed_wide/src/wide.rs

@@ -61,26 +61,3 @@ impl<A,B> WideMul<FixedI256<B>> for FixedI256<A>
 		}
 	}
 }
-
-pub enum Narrower<T>{
-	Fits(T),
-	Max,
-	Min,
-}
-
-fn tat(){
-	let a:i8=match 257i64.try_into() {
-		Ok(it) => it,
-		Err(err) => panic!(),
-	};
-}
-
-//i16 -> i8
-// 257i16.try_narrow::<i8>() -> Narrower::Max
-// 128i16.try_narrow::<i8>() -> Narrower::Fits(128i8)
-// -257i16.try_narrow::<i8>() -> Narrower::Min
-
-pub trait TryNarrow<Rhs=Self>{
-	type Output;
-	fn wide_mul(self,rhs:Rhs)->Self::Output;
-}