From 27dfb31210d6d05a68103408e39b9dd40032b2f3 Mon Sep 17 00:00:00 2001
From: Charles Cabergs <charles@cacharle.com>
Date: Wed, 7 Oct 2026 13:40:05 +0200
Subject: [PATCH] Add inplace vector support

---
 README.md                                 |  1 +
 include/rfl/parsing/VectorReader.hpp      |  9 +++++-
 include/rfl/parsing/is_inplace_vector.hpp | 37 ++++++++++++++++++++++
 include/rfl/parsing/is_vector_like.hpp    |  7 +++++
 tests/json/test_inplace_vector.cpp        | 38 +++++++++++++++++++++++
 5 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 include/rfl/parsing/is_inplace_vector.hpp
 create mode 100644 tests/json/test_inplace_vector.cpp

diff --git a/README.md b/README.md
index bc6467601..c0d73a51d 100644
--- a/README.md
+++ b/README.md
@@ -621,6 +621,7 @@ reflect-cpp supports the following containers from the C++ standard library:
 - `std::chrono::duration`
 - `std::filesystem::path`
 - `std::forward_list`
+- `std::inplace_vector` (C++26)
 - `std::map`
 - `std::multimap`
 - `std::multiset`
diff --git a/include/rfl/parsing/VectorReader.hpp b/include/rfl/parsing/VectorReader.hpp
index ac2c72c99..c7abd90d3 100644
--- a/include/rfl/parsing/VectorReader.hpp
+++ b/include/rfl/parsing/VectorReader.hpp
@@ -2,10 +2,12 @@
 #define RFL_PARSING_VECTORREADER_HPP_
 
 #include <optional>
+#include <string>
 #include <type_traits>
 
 #include "../Result.hpp"
 #include "Parser_base.hpp"
+#include "is_inplace_vector.hpp"
 #include "is_map_like.hpp"
 #include "is_set_like.hpp"
 
@@ -47,6 +49,11 @@ class VectorReader {
     const auto insert = [this](auto&& _var) -> std::optional<Error> {
       if constexpr (is_map_like_v<VecType> || is_set_like_v<VecType>) {
         vec_->insert(std::move(_var));
+      } else if constexpr (is_inplace_vector_v<VecType>) {
+        if (!vec_->try_emplace_back(std::move(_var))) {
+          return Error("Too many elements, capacity is " +
+                       std::to_string(vec_->capacity()) + ".");
+        }
       } else {
         vec_->emplace_back(std::move(_var));
       }
@@ -54,7 +61,7 @@ class VectorReader {
     };
     auto res = parse(_var).transform(insert);
     if (res) {
-      return std::nullopt;
+      return *res;
     } else {
       return res.error();
     }
diff --git a/include/rfl/parsing/is_inplace_vector.hpp b/include/rfl/parsing/is_inplace_vector.hpp
new file mode 100644
index 000000000..7e42970ab
--- /dev/null
+++ b/include/rfl/parsing/is_inplace_vector.hpp
@@ -0,0 +1,37 @@
+#ifndef RFL_PARSING_IS_INPLACE_VECTOR_HPP_
+#define RFL_PARSING_IS_INPLACE_VECTOR_HPP_
+
+#include <cstddef>
+#include <type_traits>
+
+#if __has_include(<inplace_vector>)
+#include <inplace_vector>
+#endif
+
+namespace rfl {
+namespace parsing {
+
+/**
+ * @brief Trait to check if a type is a std::inplace_vector.
+ *
+ * @tparam T The type to check.
+ */
+template <class T>
+class is_inplace_vector;
+
+template <class T>
+class is_inplace_vector : public std::false_type {};
+
+#if defined(__cpp_lib_inplace_vector)
+template <class T, std::size_t N>
+class is_inplace_vector<std::inplace_vector<T, N>> : public std::true_type {};
+#endif  // __cpp_lib_inplace_vector
+
+template <class T>
+constexpr bool is_inplace_vector_v =
+    is_inplace_vector<std::remove_cvref_t<T>>::value;
+
+}  // namespace parsing
+}  // namespace rfl
+
+#endif
diff --git a/include/rfl/parsing/is_vector_like.hpp b/include/rfl/parsing/is_vector_like.hpp
index 25cb25d36..3583608f6 100644
--- a/include/rfl/parsing/is_vector_like.hpp
+++ b/include/rfl/parsing/is_vector_like.hpp
@@ -10,6 +10,8 @@
 #include <unordered_set>
 #include <vector>
 
+#include "is_inplace_vector.hpp"
+
 namespace rfl::parsing {
 
 /**
@@ -67,6 +69,11 @@ class is_vector_like<std::unordered_set<T, Hash, KeyEqual, Allocator>>
 template <class T>
 class is_vector_like<std::vector<T>> : public std::true_type {};
 
+#if defined(__cpp_lib_inplace_vector)
+template <class T, std::size_t N>
+class is_vector_like<std::inplace_vector<T, N>> : public std::true_type {};
+#endif  // __cpp_lib_inplace_vector
+
 template <class T>
 constexpr bool is_vector_like_v = is_vector_like<std::remove_cvref_t<T>>::value;
 
diff --git a/tests/json/test_inplace_vector.cpp b/tests/json/test_inplace_vector.cpp
new file mode 100644
index 000000000..fc010f3be
--- /dev/null
+++ b/tests/json/test_inplace_vector.cpp
@@ -0,0 +1,38 @@
+#include <rfl.hpp>
+#include <rfl/json.hpp>
+#include <string>
+
+#include "write_and_read.hpp"
+
+#if __has_include(<inplace_vector>)
+#include <inplace_vector>
+#endif
+
+#if defined(__cpp_lib_inplace_vector)
+
+namespace test_inplace_vector {
+
+struct Person {
+  rfl::Rename<"firstName", std::string> first_name;
+  rfl::Rename<"lastName", std::string> last_name = "Simpson";
+  std::inplace_vector<std::string, 3> children;
+};
+
+TEST(json, test_inplace_vector) {
+  const auto homer =
+      Person{.first_name = "Homer", .children = {"Bart", "Lisa", "Maggie"}};
+
+  write_and_read(
+      homer,
+      R"({"firstName":"Homer","lastName":"Simpson","children":["Bart","Lisa","Maggie"]})");
+}
+
+TEST(json, test_inplace_vector_overflow) {
+  const auto res = rfl::json::read<Person>(
+      R"({"firstName":"Homer","children":["Bart","Lisa","Maggie","Hugo"]})");
+  EXPECT_FALSE(res && true);
+}
+
+}  // namespace test_inplace_vector
+
+#endif  // __cpp_lib_inplace_vector