From f02c8b8e29842a5432e50e635fb1e703aa094648 Mon Sep 17 00:00:00 2001
From: MagisterDaIlis <196101336+MagisterDaIlis@users.noreply.github.com>
Date: Mon, 27 Jan 2025 08:24:34 +0100
Subject: [PATCH] feat(corelib): Iterator::Sum (#7142)

---
 corelib/src/iter.cairo                 |  2 +-
 corelib/src/iter/traits.cairo          |  2 +-
 corelib/src/iter/traits/accum.cairo    | 19 ++++++++++++++++
 corelib/src/iter/traits/iterator.cairo | 30 +++++++++++++++++++++++++-
 corelib/src/test/iter_test.cairo       |  6 ++++++
 5 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/corelib/src/iter.cairo b/corelib/src/iter.cairo
index 8220190bbf1..a0d75e911f0 100644
--- a/corelib/src/iter.cairo
+++ b/corelib/src/iter.cairo
@@ -232,4 +232,4 @@
 mod adapters;
 mod traits;
 pub use adapters::PeekableTrait;
-pub use traits::{FromIterator, IntoIterator, Iterator, Product};
+pub use traits::{FromIterator, IntoIterator, Iterator, Product, Sum};
diff --git a/corelib/src/iter/traits.cairo b/corelib/src/iter/traits.cairo
index 57a8e5fac7a..d44e90b26e3 100644
--- a/corelib/src/iter/traits.cairo
+++ b/corelib/src/iter/traits.cairo
@@ -1,6 +1,6 @@
 mod accum;
 mod collect;
 mod iterator;
-pub use accum::Product;
+pub use accum::{Product, Sum};
 pub use collect::{FromIterator, IntoIterator};
 pub use iterator::Iterator;
diff --git a/corelib/src/iter/traits/accum.cairo b/corelib/src/iter/traits/accum.cairo
index e0e0bcb1a92..129a76dfc8b 100644
--- a/corelib/src/iter/traits/accum.cairo
+++ b/corelib/src/iter/traits/accum.cairo
@@ -1,3 +1,22 @@
+/// Trait to represent types that can be created by summing up an iterator.
+///
+/// This trait is used to implement [`Iterator::sum()`]. Types which implement
+/// this trait can be generated by using the [`sum()`] method on an iterator.
+/// Like [`FromIterator`], this trait should rarely be called directly.
+///
+/// [`sum()`]: crate::iter::Iterator::sum
+/// [`FromIterator`]: crate::iter::FromIterator
+pub trait Sum<A> {
+    /// Takes an iterator and generates `Self` from the elements by "summing up"
+    /// the items.
+    fn sum<I, +Iterator<I>[Item: A], +Destruct<I>, +Destruct<A>>(iter: I) -> A;
+}
+
+impl SumAddableTypesImpl<A, +Add<A>, impl ZeroA: core::num::traits::Zero<A>> of Sum<A> {
+    fn sum<I, +Iterator<I>[Item: A], +Destruct<I>, +Destruct<A>>(mut iter: I) -> A {
+        iter.fold(ZeroA::zero(), |acc, x| acc + x)
+    }
+}
 /// Trait to represent types that can be created by multiplying elements of an
 /// iterator.
 ///
diff --git a/corelib/src/iter/traits/iterator.cairo b/corelib/src/iter/traits/iterator.cairo
index 10d42cc4239..b1996bc05ab 100644
--- a/corelib/src/iter/traits/iterator.cairo
+++ b/corelib/src/iter/traits/iterator.cairo
@@ -2,7 +2,7 @@ use crate::iter::adapters::{
     Enumerate, Map, Peekable, Zip, enumerated_iterator, mapped_iterator, peekable_iterator,
     zipped_iterator,
 };
-use crate::iter::traits::Product;
+use crate::iter::traits::{Product, Sum};
 
 /// A trait for dealing with iterators.
 ///
@@ -473,6 +473,34 @@ pub trait Iterator<T> {
         peekable_iterator(self)
     }
 
+    /// Sums the elements of an iterator.
+    ///
+    /// Takes each element, adds them together, and returns the result.
+    ///
+    /// An empty iterator returns the zero value of the type.
+    ///
+    /// `sum()` can be used to sum any type implementing [`Sum`][`core::iter::Sum`],
+    /// including [`Option`][`Option::sum`] and [`Result`][`Result::sum`].
+    ///
+    /// # Panics
+    ///
+    /// When calling `sum()` and a primitive integer type is being returned, this
+    /// method will panic if the computation overflows.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut iter = array![1, 2, 3].into_iter();
+    /// let sum: usize = iter.sum();
+    ///
+    /// assert_eq!(sum, 6);
+    /// ```
+    fn sum<+Destruct<T>, +Destruct<Self::Item>, +Sum<Self::Item>>(
+        self: T,
+    ) -> Self::Item {
+        Sum::<Self::Item>::sum::<T, Self>(self)
+    }
+
     /// Iterates over the entire iterator, multiplying all the elements
     ///
     /// An empty iterator returns the one value of the type.
diff --git a/corelib/src/test/iter_test.cairo b/corelib/src/test/iter_test.cairo
index c1111bae772..b2615c1ca93 100644
--- a/corelib/src/test/iter_test.cairo
+++ b/corelib/src/test/iter_test.cairo
@@ -98,6 +98,12 @@ fn test_iter_adapter_peekable() {
     assert_eq!(iter.next(), Option::None);
 }
 
+#[test]
+fn test_iter_accum_sum() {
+    assert_eq!(array![1, 2, 3].into_iter().sum(), 6);
+    assert_eq!(array![].into_iter().sum(), 0);
+}
+
 #[test]
 fn test_iter_accum_product() {
     assert_eq!((1_usize..=0).into_iter().product(), 1);