From 07f1b20e26b87b041123f6dec07675cf57422f91 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Tue, 1 Sep 2026 05:29:01 +0000
Subject: [PATCH] Take the output adapter by reference at the serializer ctor

Per review: the serializer still holds the adapter as a non-owning
pointer, but the constructor now takes output_adapter_protocol<char>&
and takes its address internally, so every call site passes a
reference. A reference cannot be null and reads as a borrow, which
makes the lifetime contract harder to get wrong than handing over a
raw pointer. The stored member and the write path are unchanged.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
---
 include/nlohmann/detail/output/serializer.hpp |  4 ++--
 include/nlohmann/json.hpp                     |  6 +++---
 single_include/nlohmann/json.hpp              | 10 +++++-----
 tests/src/unit-convenience.cpp                |  2 +-
 4 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/nlohmann/detail/output/serializer.hpp b/include/nlohmann/detail/output/serializer.hpp
index 3ea359109..9560729ad 100644
--- a/include/nlohmann/detail/output/serializer.hpp
+++ b/include/nlohmann/detail/output/serializer.hpp
@@ -77,12 +77,12 @@ class serializer
     being threaded through every call to @ref dump, @ref dump_internal and
     @ref dump_iteratively.
     */
-    serializer(output_adapter_protocol<char>* s, const char ichar,
+    serializer(output_adapter_protocol<char>& s, const char ichar,
                const bool pretty_print_ = false,
                const bool ensure_ascii_ = false,
                const std::size_t indent_step_ = 0,
                error_handler_t error_handler_ = error_handler_t::strict)
-        : o(s)
+        : o(&s)
         , locale(std::localeconv())
         , indent_char(ichar)
         , pretty_print(pretty_print_)
diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp
index 48cf3c4b0..016a4dd27 100644
--- a/include/nlohmann/json.hpp
+++ b/include/nlohmann/json.hpp
@@ -1347,13 +1347,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (indent >= 0)
         {
-            serializer s(&string_adapter, indent_char,
+            serializer s(string_adapter, indent_char,
                          true, ensure_ascii, static_cast<std::size_t>(indent), error_handler);
             s.dump(*this);
         }
         else
         {
-            serializer s(&string_adapter, indent_char,
+            serializer s(string_adapter, indent_char,
                          false, ensure_ascii, 0, error_handler);
             s.dump(*this);
         }
@@ -4085,7 +4085,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         // do the actual serialization
         detail::output_stream_adapter<char> stream_adapter(o);
-        serializer s(&stream_adapter, o.fill(),
+        serializer s(stream_adapter, o.fill(),
                      pretty_print, false, static_cast<std::size_t>(indentation));
         s.dump(j);
         return o;
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index b3fcd6cdd..c94c477ed 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -21425,12 +21425,12 @@ class serializer
     being threaded through every call to @ref dump, @ref dump_internal and
     @ref dump_iteratively.
     */
-    serializer(output_adapter_protocol<char>* s, const char ichar,
+    serializer(output_adapter_protocol<char>& s, const char ichar,
                const bool pretty_print_ = false,
                const bool ensure_ascii_ = false,
                const std::size_t indent_step_ = 0,
                error_handler_t error_handler_ = error_handler_t::strict)
-        : o(s)
+        : o(&s)
         , locale(std::localeconv())
         , indent_char(ichar)
         , pretty_print(pretty_print_)
@@ -24743,13 +24743,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         if (indent >= 0)
         {
-            serializer s(&string_adapter, indent_char,
+            serializer s(string_adapter, indent_char,
                          true, ensure_ascii, static_cast<std::size_t>(indent), error_handler);
             s.dump(*this);
         }
         else
         {
-            serializer s(&string_adapter, indent_char,
+            serializer s(string_adapter, indent_char,
                          false, ensure_ascii, 0, error_handler);
             s.dump(*this);
         }
@@ -27481,7 +27481,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         // do the actual serialization
         detail::output_stream_adapter<char> stream_adapter(o);
-        serializer s(&stream_adapter, o.fill(),
+        serializer s(stream_adapter, o.fill(),
                      pretty_print, false, static_cast<std::size_t>(indentation));
         s.dump(j);
         return o;
diff --git a/tests/src/unit-convenience.cpp b/tests/src/unit-convenience.cpp
index fcf6ba73c..0ba57d846 100644
--- a/tests/src/unit-convenience.cpp
+++ b/tests/src/unit-convenience.cpp
@@ -99,7 +99,7 @@ void check_escaped(const char* original, const char* escaped, const bool ensure_
 {
     std::stringstream ss;
     nlohmann::detail::output_stream_adapter<char> adapter(ss);
-    json::serializer s(&adapter, ' ', false, ensure_ascii);
+    json::serializer s(adapter, ' ', false, ensure_ascii);
     s.dump_escaped(original);
     s.flush(); // dump_escaped writes into the serializer's internal buffer
     CHECK(ss.str() == escaped);