From 0369e64b56346f04aaaea60c159761651424f336 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Thu, 28 Nov 2024 15:51:29 +1100
Subject: [PATCH] Implement Sum for an iterator of references to amounts

We have `iter::Sum` already for `Amount` and `SignedAmount`. Add
an implementation for each to support iterators that yield references.
---
 units/src/amount/signed.rs   | 10 ++++++++++
 units/src/amount/tests.rs    |  4 ++--
 units/src/amount/unsigned.rs | 10 ++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/units/src/amount/signed.rs b/units/src/amount/signed.rs
index b90fdd5e7..841b27071 100644
--- a/units/src/amount/signed.rs
+++ b/units/src/amount/signed.rs
@@ -442,6 +442,16 @@ impl core::iter::Sum for SignedAmount {
     }
 }
 
+impl<'a> core::iter::Sum<&'a SignedAmount> for SignedAmount {
+    fn sum<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = &'a SignedAmount>,
+    {
+        let sats: i64 = iter.map(|amt| amt.0).sum();
+        SignedAmount::from_sat(sats)
+    }
+}
+
 #[cfg(feature = "arbitrary")]
 impl<'a> Arbitrary<'a> for SignedAmount {
     fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
diff --git a/units/src/amount/tests.rs b/units/src/amount/tests.rs
index e695a443b..00d54d726 100644
--- a/units/src/amount/tests.rs
+++ b/units/src/amount/tests.rs
@@ -825,8 +825,8 @@ fn serde_as_sat_opt() {
 
 #[test]
 fn sum_amounts() {
-    assert_eq!(Amount::from_sat(0), [].into_iter().sum::<Amount>());
-    assert_eq!(SignedAmount::from_sat(0), [].into_iter().sum::<SignedAmount>());
+    assert_eq!(Amount::from_sat(0), [].iter().sum::<Amount>());
+    assert_eq!(SignedAmount::from_sat(0), [].iter().sum::<SignedAmount>());
 
     let amounts = [Amount::from_sat(42), Amount::from_sat(1337), Amount::from_sat(21)];
     let sum = amounts.into_iter().sum::<Amount>();
diff --git a/units/src/amount/unsigned.rs b/units/src/amount/unsigned.rs
index a68262385..143c94e57 100644
--- a/units/src/amount/unsigned.rs
+++ b/units/src/amount/unsigned.rs
@@ -432,6 +432,16 @@ impl core::iter::Sum for Amount {
     }
 }
 
+impl<'a> core::iter::Sum<&'a Amount> for Amount {
+    fn sum<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = &'a Amount>,
+    {
+        let sats: u64 = iter.map(|amt| amt.0).sum();
+        Amount::from_sat(sats)
+    }
+}
+
 #[cfg(feature = "arbitrary")]
 impl<'a> Arbitrary<'a> for Amount {
     fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {