From 3d7ba40289f46526db4e5269f32655e0b242b47b Mon Sep 17 00:00:00 2001
From: Kurt Sassenrath <kurt@sassenrath.me>
Date: Sat, 30 Dec 2023 19:18:09 -0800
Subject: [PATCH] Add msgpack packer support for ranges of objects.

---
 .../core/detail/builtin_packable_types.h      | 84 +++++++++----------
 .../msgpack/core/detail/packable_ranges.h     | 20 ++++-
 include/parselink/msgpack/core/packer.h       | 11 +--
 3 files changed, 64 insertions(+), 51 deletions(-)

diff --git a/include/parselink/msgpack/core/detail/builtin_packable_types.h b/include/parselink/msgpack/core/detail/builtin_packable_types.h
index dcc3777..1a2fb44 100644
--- a/include/parselink/msgpack/core/detail/builtin_packable_types.h
+++ b/include/parselink/msgpack/core/detail/builtin_packable_types.h
@@ -38,6 +38,10 @@ constexpr auto pack_integral(T value, Itr out, std::size_t sz) noexcept {
     return out;
 }
 
+struct dummy_packer {
+    std::byte* out;
+};
+
 // Defines a range of bytes for binary formats.
 template <typename T>
 concept byte_range = std::ranges::contiguous_range<T>
@@ -66,25 +70,23 @@ struct builtin_packer;
 
 template <>
 struct builtin_packer<invalid> : builtin_packer_base {
-    static constexpr auto pack(auto, auto out) noexcept -> decltype(out) {
-        *out++ = format::invalid::marker;
-        return out;
+    static constexpr void pack(auto, auto& packer) noexcept {
+        *(packer.out)++ = format::invalid::marker;
     }
 };
 
 template <>
 struct builtin_packer<nil> : builtin_packer_base {
-    static constexpr auto pack(auto, auto out) noexcept -> decltype(out) {
-        *out++ = format::nil::marker;
-        return out;
+    static constexpr void pack(auto, auto& packer) noexcept {
+        *(packer.out)++ = format::nil::marker;
     }
 };
 
 template <>
 struct builtin_packer<bool> : builtin_packer_base {
-    static constexpr auto pack(bool value, auto out) noexcept -> decltype(out) {
-        *out++ = format::boolean::marker | static_cast<std::byte>(value);
-        return out;
+    static constexpr void pack(bool value, auto& packer) noexcept {
+        *(packer.out)++ =
+                format::boolean::marker | static_cast<std::byte>(value);
     }
 };
 
@@ -109,10 +111,9 @@ struct builtin_packer<T> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(
-            T const& value, auto out) noexcept -> decltype(out) {
-        *out++ = marker(value);
-        return detail::pack_integral(value, out, rep_size(value));
+    static constexpr void pack(T const& value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
+        packer.out = detail::pack_integral(value, packer.out, rep_size(value));
     }
 };
 
@@ -144,10 +145,9 @@ struct builtin_packer<T> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(
-            T const& value, auto out) noexcept -> decltype(out) {
-        *out++ = marker(value);
-        return detail::pack_integral(value, out, rep_size(value));
+    static constexpr void pack(T const& value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
+        packer.out = detail::pack_integral(value, packer.out, rep_size(value));
     }
 };
 
@@ -175,12 +175,11 @@ struct builtin_packer<T> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(
-            T const& value, auto out) noexcept -> decltype(out) {
-        *out++ = marker(value);
-        out = detail::pack_integral(
-                std::ranges::size(value), out, len_size(value));
-        return std::ranges::copy(value, out).out;
+    static constexpr void pack(T const& value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
+        packer.out = detail::pack_integral(
+                std::ranges::size(value), packer.out, len_size(value));
+        packer.out = std::ranges::copy(value, packer.out).out;
     }
 };
 
@@ -211,13 +210,12 @@ struct builtin_packer<std::string_view> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(
-            std::string_view value, auto out) noexcept -> decltype(out) {
-        *out++ = marker(value);
+    static constexpr void pack(std::string_view value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
         auto const size = std::size(value);
-        out = detail::pack_integral(size, out, len_size(value));
+        packer.out = detail::pack_integral(size, packer.out, len_size(value));
         auto const* beg = reinterpret_cast<std::byte const*>(&*value.begin());
-        return std::ranges::copy(beg, beg + size, out).out;
+        packer.out = std::ranges::copy(beg, beg + size, packer.out).out;
     }
 };
 
@@ -249,9 +247,10 @@ struct builtin_packer<array_desc> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(array_desc value, auto out) noexcept {
-        *out++ = marker(value);
-        return detail::pack_integral(value.count, out, rep_size(value));
+    static constexpr auto pack(array_desc value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
+        packer.out =
+                detail::pack_integral(value.count, packer.out, rep_size(value));
     }
 };
 
@@ -278,21 +277,22 @@ struct builtin_packer<map_desc> : builtin_packer_base {
         }
     }
 
-    static constexpr auto pack(map_desc value, auto out) noexcept {
-        *out++ = marker(value);
-        return detail::pack_integral(value.count, out, rep_size(value));
+    static constexpr void pack(map_desc value, auto& packer) noexcept {
+        *(packer.out)++ = marker(value);
+        packer.out =
+                detail::pack_integral(value.count, packer.out, rep_size(value));
     }
 };
 
-/* template <> */
-/* struct builtin_packer<map_desc> */
-/*         : builtin_packer_base<format::type::map> {}; */
-
 // Requirements for builtin_packable types.
-template <typename T>
-concept builtin_packable = requires(T const& value, std::byte* dest) {
-    { builtin_packer<T>::total_size(value) } -> std::same_as<std::size_t>;
-    { builtin_packer<T>::pack(value, dest) } -> std::same_as<decltype(dest)>;
+template <typename T, typename Packer = detail::dummy_packer>
+concept builtin_packable = requires(T&& value, Packer& dest) {
+    {
+        builtin_packer<std::remove_cvref_t<T>>::total_size(value)
+    } -> std::same_as<std::size_t>;
+    {
+        builtin_packer<std::remove_cvref_t<T>>::pack(value, dest)
+    } -> std::same_as<void>;
 };
 
 } // namespace msgpack
diff --git a/include/parselink/msgpack/core/detail/packable_ranges.h b/include/parselink/msgpack/core/detail/packable_ranges.h
index 93b60f3..8e1ef3c 100644
--- a/include/parselink/msgpack/core/detail/packable_ranges.h
+++ b/include/parselink/msgpack/core/detail/packable_ranges.h
@@ -31,11 +31,23 @@ template <typename T>
 concept packable_range = std::ranges::input_range<T>
                       && builtin_packable<std::ranges::range_value_t<T>>;
 
-static_assert(packable_range<std::array<std::string_view, 5>>);
-static_assert(packable_range<std::span<std::string_view>>);
-
 template <packable_range T>
-struct builtin_packer<T> {
+struct builtin_packer<T> : builtin_packer_base {
+    static constexpr std::size_t rep_size(T const& value) {
+        return std::ranges::size(value);
+    }
+
+    static constexpr auto marker(T const& value) {
+        array_desc desc(rep_size(value));
+        return builtin_packer<array_desc>::marker(desc);
+    }
+
+    static constexpr void pack(T const& value, auto& packer) noexcept {
+        packer.pack(array_desc(rep_size(value)));
+        for (auto const& element : value) {
+            packer.pack(element);
+        }
+    }
 };
 
 } // namespace msgpack
diff --git a/include/parselink/msgpack/core/packer.h b/include/parselink/msgpack/core/packer.h
index 6998ee6..05a67d4 100644
--- a/include/parselink/msgpack/core/packer.h
+++ b/include/parselink/msgpack/core/packer.h
@@ -39,6 +39,7 @@
 #define msgpack_core_packer_1d5939e9c1498568
 
 #include "parselink/msgpack/core/detail/builtin_packable_types.h"
+#include "parselink/msgpack/core/detail/packable_ranges.h"
 #include "parselink/msgpack/core/error.h"
 #include "parselink/msgpack/core/format.h"
 #include "parselink/msgpack/util/endianness.h"
@@ -75,9 +76,7 @@ public:
         }
 
         template <packable_type T>
-        constexpr tl::expected<tl::monostate, error> pack(T&& v) noexcept {
-            using diff_type =
-                    std::iterator_traits<decltype(curr_)>::difference_type;
+        constexpr tl::expected<tl::monostate, error> pack(T const& v) noexcept {
             auto rem = remaining();
             decltype(rem) needed = builtin_packer<T>::total_size(v);
             if (needed > rem) {
@@ -93,10 +92,12 @@ public:
     constexpr tl::expected<tl::monostate, error> pack(T&& v) noexcept {
         context ctx{curr_, end_};
         // If packing is successful, it updates iterators.
-        return ctx.pack(std::forward<T>(v)).map([&]{
+        auto ret = ctx.pack(std::forward<T>(v));
+        if (!!ret) {
             curr_ = ctx.out;
             end_ = ctx.end;
-        });
+        }
+        return ret;
     }
 
     constexpr auto tell() const noexcept {