split_from: use REAL generics

src/misc.rs

@@ -2,11 +2,7 @@ use std::{iter::Rev, ops::RangeInclusive};
 
 pub fn split_from<T>(min: T, max: T, x: T) -> Vec<Vec<T>>
 where
-    T: std::cmp::PartialOrd
-        + std::ops::Add<usize, Output = T>
-        + std::ops::Sub<usize, Output = T>
-        + Copy
-        + Ord,
+    T: num::Integer + Copy,
     RangeInclusive<T>: Iterator<Item = T> + DoubleEndedIterator,
     Rev<RangeInclusive<T>>: Iterator<Item = T>,
 {
@@ -14,15 +10,14 @@ where
         return Vec::new();
     }
 
-    let x_upper = (x + 1).min(max);
-
-    let mut output: Vec<Vec<T>> = Vec::new();
-    if x > min + 1 {
-        let x_lower = x - 1;
+    let mut output: Vec<Vec<T>> = Vec::with_capacity(2);
+    if x > min + T::one() {
+        let x_lower = x - T::one();
         output.push((min..=x_lower).rev().collect());
     }
-    if x_upper < max {
-        output.push((x_upper..=max).collect());
+
+    if x + T::one() < max {
+        output.push(((x + T::one())..=max).collect());
     }
     output
 }
@@ -38,5 +33,8 @@ mod test {
         assert_eq!(split_from(0, 6, 0), vec![vec![1, 2, 3, 4, 5, 6]]);
 
         assert_eq!(split_from(0, 6, 6), vec![vec![5, 4, 3, 2, 1, 0]]);
+
+        // test out-of-bounds and also generics
+        assert_eq!(split_from::<i16>(-1, 4, 10), Vec::<Vec<i16>>::new());
     }
 }