From abc04f2ee57bd901e199a75f906b5b94682bdc49 Mon Sep 17 00:00:00 2001
From: "Keith A. Lewis" <kal@kalx.net>
Date: Thu, 13 Jun 2024 13:58:59 -0400
Subject: [PATCH] counted pointer

---
 fms_iterable.h     | 23 ++++++++++++++++++-----
 fms_iterable.t.cpp | 47 ++++++++++++++++++++++++++++++++--------------
 2 files changed, 51 insertions(+), 19 deletions(-)

diff --git a/fms_iterable.h b/fms_iterable.h
index abc3698..9733997 100644
--- a/fms_iterable.h
+++ b/fms_iterable.h
@@ -584,26 +584,36 @@ namespace fms::iterable {
 		}
 	};
 
-	// Unsafe pointer interface.
+	// Unsafe counted pointer interface with std::span semantics.
 	template <class T>
 	class pointer {
 		T* p;
+		size_t n;
 	public:
 		using iterator_category = std::input_iterator_tag;
 		using value_type = T;
 		using reference = T&;
 		using difference_type = std::ptrdiff_t;
 
-		// pointer() is empty iterator
-		pointer(T* p = nullptr) noexcept
-			: p(p)
+		// possible unsafe
+		pointer(T* p, size_t n = std::numeric_limits<size_t>::max()) noexcept
+			: p(p), n(n)
 		{ }
 
 		bool operator==(const pointer& _p) const = default;
 
+		auto begin() const
+		{
+			return *this;
+		}
+		auto end() const
+		{
+			return pointer<T>(p + n, 0);
+		}
+
 		explicit operator bool() const noexcept
 		{
-			return p != nullptr; // unsafe
+			return n != 0; // possibly unsafe
 		}
 		value_type operator*() const noexcept
 		{
@@ -616,6 +626,9 @@ namespace fms::iterable {
 		pointer& operator++() noexcept
 		{
 			++p;
+			if (n > 0) {
+				--n;
+			}
 
 			return *this;
 		}
diff --git a/fms_iterable.t.cpp b/fms_iterable.t.cpp
index d6d0b2f..3220ada 100644
--- a/fms_iterable.t.cpp
+++ b/fms_iterable.t.cpp
@@ -320,20 +320,39 @@ int test_fold() {
 }
 
 int test_pointer() {
-	int i[] = { 1, 2, 3 };
-	pointer p(i);
-	pointer p2(p);
-	assert(p == p2);
-	p = p2;
-	assert(!(p2 != p));
-
-	assert(p);
-	assert(*p == 1);
-	++p;
-	assert(*p == 2);
-	++p;
-	assert(*p == 3);
-	++p; // *p is undefined
+	{
+		int i[] = { 1, 2, 3 };
+		pointer p(i);
+		pointer p2(p);
+		assert(p == p2);
+		p = p2;
+		assert(!(p2 != p));
+
+		assert(p);
+		assert(*p == 1);
+		++p;
+		assert(*p == 2);
+		++p;
+		assert(*p == 3);
+		++p; // *p is undefined
+	}
+	{
+		int i[] = { 1, 2, 3 };
+		pointer p(i, 3);
+		pointer p2(p);
+		assert(p == p2);
+		p = p2;
+		assert(!(p2 != p));
+
+		assert(p);
+		assert(*p == 1);
+		++p;
+		assert(*p == 2);
+		++p;
+		assert(*p == 3);
+		++p;
+		assert(!p);
+	}
 
 	return 0;
 }