fix comments, use i32, simplify arms

zebra-chain/src/block/height.rs

@@ -4,6 +4,10 @@ use std::ops::{Add, Sub};
 
 /// The height of a block is the length of the chain back to the genesis block.
 ///
+/// Block heights can't be added, but they can be *subtracted*,
+/// to get a difference of block heights, represented as an `i32`,
+/// and height differences can be added to block heights to get new heights.
+///
 /// # Invariants
 ///
 /// Users should not construct block heights greater than `Height::MAX`.
@@ -43,50 +47,34 @@ impl Height {
     pub const MAX_AS_U32: u32 = Self::MAX.0;
 }
 
-// Block heights live in a torsor, they can only be contructed but not computed directly.
-// Addition and substraction is done in the underlying types(u32) and not in the heights themselves.
-// This u32 numbers are a group and they can be added and substracted normally to get a new integer.
-// Having the result of the computation the `Height(X)` constructor can be used to build a new `Height`.
-
-// N = Height1.U - Height2.U
-// Given two `Height`s use the underlying value of them to compute the difference,
-// return this number as it is.
 impl Sub<Height> for Height {
-    type Output = Option<u32>;
+    type Output = i32;
 
-    fn sub(self, rhs: Height) -> Option<u32> {
-        self.0.checked_sub(rhs.0)
+    fn sub(self, rhs: Height) -> i32 {
+        (self.0 as i32) - (rhs.0 as i32)
     }
 }
 
-// H = Height(Height.U + N)
-// Given a `Height` and a number, sum the underlying value to the number,
-// with the result construct a new `Height` and return it.
-impl Add<u32> for Height {
+impl Add<i32> for Height {
     type Output = Option<Height>;
 
-    fn add(self, rhs: u32) -> Option<Height> {
-        let result = self.0.checked_add(rhs);
+    fn add(self, rhs: i32) -> Option<Height> {
+        let result = ((self.0 as i32) + rhs) as u32;
         match result {
-            Some(h) if (Height(h) <= Height::MAX) => Some(Height(h)),
-            Some(_) => None,
-            None => None,
+            h if (Height(h) <= Height::MAX && Height(h) >= Height::MIN) => Some(Height(h)),
+            _ => None,
         }
     }
 }
 
-// H = Height(Height.U - N)
-// Given a `Height` and a number, substract the number to the underlying value,
-// with the result construct a new `Height` and return it.
-impl Sub<u32> for Height {
+impl Sub<i32> for Height {
     type Output = Option<Height>;
 
-    fn sub(self, rhs: u32) -> Option<Height> {
-        let result = self.0.checked_sub(rhs);
+    fn sub(self, rhs: i32) -> Option<Height> {
+        let result = ((self.0 as i32) - rhs) as u32;
         match result {
-            Some(h) if (Height(h) >= Height::MIN) => Some(Height(h)),
-            Some(_) => None,
-            None => None,
+            h if (Height(h) <= Height::MAX && Height(h) >= Height::MIN) => Some(Height(h)),
+            _ => None,
         }
     }
 }
@@ -113,7 +101,7 @@ fn operator_tests() {
     assert_eq!(Some(Height(0)), Height(1) - 1);
     assert_eq!(None, Height(0) - 1);
 
-    assert_eq!(Some(1), Height(2) - Height(1));
-    assert_eq!(Some(0), Height(1) - Height(1));
-    assert_eq!(None, Height(0) - Height(1));
+    assert_eq!(1, Height(2) - Height(1));
+    assert_eq!(0, Height(1) - Height(1));
+    assert_eq!(-1, Height(0) - Height(1));
 }