From 10a7e83461ac62b8d51981c3cfaeac584700417f Mon Sep 17 00:00:00 2001
From: "Keith A. Lewis" <kal@kalx.net>
Date: Sat, 1 Jun 2024 17:01:46 -0400
Subject: [PATCH] pair

---
 fms_iterable.h     | 29 +++++++++++++++++++++++++++++
 fms_iterable.t.cpp | 14 ++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/fms_iterable.h b/fms_iterable.h
index c2b03a9..cd1874b 100644
--- a/fms_iterable.h
+++ b/fms_iterable.h
@@ -1271,6 +1271,35 @@ namespace fms::iterable {
 		return delta(i, [](T a, T b) { return std::min<T>(b - a, 0); });
 	}
 
+	template<input I, input J>
+	class pair {
+		I i;
+		J j;
+	public:
+		using iterator_category = std::input_iterator_tag;
+		using value_type = std::pair<typename I::value_type, typename J::value_type>;
+
+		pair(I i, J j)
+			: i(i), j(j)
+		{ }
+
+		explicit operator bool() const
+		{
+			return i and j;
+		}
+		value_type operator*() const
+		{
+			return { *i, *j };
+		}
+		pair& operator++()
+		{
+			++i;
+			++j;
+
+			return *this;
+		}
+	};
+
 } // namespace fms::iterable
 
 #define FMS_ITERABLE_OPERATOR(X) \
diff --git a/fms_iterable.t.cpp b/fms_iterable.t.cpp
index e7af33e..df88316 100644
--- a/fms_iterable.t.cpp
+++ b/fms_iterable.t.cpp
@@ -695,6 +695,19 @@ int test_exp() {
 
 	return 0;
 }
+int test_pair()
+{
+	{
+		pair p(iota(1), iota(2));
+		assert(p);
+		assert(*p == std::make_pair(1,2));
+
+		++p;
+		assert(p);
+		assert(*p == std::make_pair(2, 3));
+	}
+	return 0;
+}
 
 int main()
 {
@@ -721,6 +734,7 @@ int main()
 	test_delta();
 	test_call();
 	test_exp();
+	test_pair();
 
 	return 0;
 }