units: Add assign macros

Add macros for implementing `ops::AddAssign` and `ops::SubAssign`. Use
them in `fee_rate`.

Refactor only, no logic changes.

units/src/fee_rate.rs

@@ -190,6 +190,7 @@ impl ops::Add for FeeRate {
     fn add(self, rhs: FeeRate) -> Self::Output { FeeRate(self.0 + rhs.0) }
 }
 crate::internal_macros::impl_add_for_references!(FeeRate);
+crate::internal_macros::impl_add_assign!(FeeRate);
 
 impl ops::Sub for FeeRate {
     type Output = FeeRate;
@@ -197,6 +198,7 @@ impl ops::Sub for FeeRate {
     fn sub(self, rhs: FeeRate) -> Self::Output { FeeRate(self.0 - rhs.0) }
 }
 crate::internal_macros::impl_sub_for_references!(FeeRate);
+crate::internal_macros::impl_sub_assign!(FeeRate);
 
 /// Computes the ceiling so that the fee computation is conservative.
 impl ops::Mul<FeeRate> for Weight {
@@ -223,22 +225,6 @@ impl ops::Div<Weight> for Amount {
     fn div(self, rhs: Weight) -> Self::Output { FeeRate(self.to_sat() * 1000 / rhs.to_wu()) }
 }
 
-impl ops::AddAssign for FeeRate {
-    fn add_assign(&mut self, rhs: Self) { self.0 += rhs.0 }
-}
-
-impl ops::AddAssign<&FeeRate> for FeeRate {
-    fn add_assign(&mut self, rhs: &FeeRate) { self.0 += rhs.0 }
-}
-
-impl ops::SubAssign for FeeRate {
-    fn sub_assign(&mut self, rhs: Self) { self.0 -= rhs.0 }
-}
-
-impl ops::SubAssign<&FeeRate> for FeeRate {
-    fn sub_assign(&mut self, rhs: &FeeRate) { self.0 -= rhs.0 }
-}
-
 impl core::iter::Sum for FeeRate {
     fn sum<I>(iter: I) -> Self
     where

units/src/internal_macros.rs

@@ -34,6 +34,20 @@ macro_rules! impl_add_for_references {
 }
 pub(crate) use impl_add_for_references;
 
+/// Implement `ops::AddAssign` for `$ty` and `&$ty`.
+macro_rules! impl_add_assign {
+    ($ty:ident) => {
+         impl core::ops::AddAssign<$ty> for $ty {
+            fn add_assign(&mut self, rhs: $ty) { *self = *self + rhs }
+        }
+
+        impl core::ops::AddAssign<&$ty> for $ty {
+            fn add_assign(&mut self, rhs: &$ty) { *self = *self + *rhs }
+        }
+    }
+}
+pub(crate) use impl_add_assign;
+
 /// Implement `ops::Sub` for various references.
 ///
 /// Requires `$ty` it implement `Sub` e.g. 'impl Sub<T> for T'. Adds impls of:
@@ -63,3 +77,17 @@ macro_rules! impl_sub_for_references {
     }
 }
 pub(crate) use impl_sub_for_references;
+
+/// Implement `ops::SubAssign` for `$ty` and `&$ty`.
+macro_rules! impl_sub_assign {
+    ($ty:ident) => {
+         impl core::ops::SubAssign<$ty> for $ty {
+            fn sub_assign(&mut self, rhs: $ty) { *self = *self - rhs }
+        }
+
+        impl core::ops::SubAssign<&$ty> for $ty {
+            fn sub_assign(&mut self, rhs: &$ty) { *self = *self - *rhs }
+        }
+   }
+}
+pub(crate) use impl_sub_assign;