Allow allocators for output_vector_adapter (#2989)

* ♻ allow allocators for vectors

* ✅ add regression tests

include/nlohmann/detail/output/output_adapters.hpp

@@ -37,11 +37,11 @@ template<typename CharType>
 using output_adapter_t = std::shared_ptr<output_adapter_protocol<CharType>>;
 
 /// output adapter for byte vectors
-template<typename CharType>
+template<typename CharType, typename AllocatorType = std::allocator<CharType>>
 class output_vector_adapter : public output_adapter_protocol<CharType>
 {
   public:
-    explicit output_vector_adapter(std::vector<CharType>& vec) noexcept
+    explicit output_vector_adapter(std::vector<CharType, AllocatorType>& vec) noexcept
         : v(vec)
     {}
 
@@ -57,7 +57,7 @@ class output_vector_adapter : public output_adapter_protocol<CharType>
     }
 
   private:
-    std::vector<CharType>& v;
+    std::vector<CharType, AllocatorType>& v;
 };
 
 #ifndef JSON_NO_IO
@@ -114,8 +114,9 @@ template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_adapter
 {
   public:
-    output_adapter(std::vector<CharType>& vec)
-        : oa(std::make_shared<output_vector_adapter<CharType>>(vec)) {}
+    template<typename AllocatorType = std::allocator<CharType>>
+    output_adapter(std::vector<CharType, AllocatorType>& vec)
+        : oa(std::make_shared<output_vector_adapter<CharType, AllocatorType>>(vec)) {}
 
 #ifndef JSON_NO_IO
     output_adapter(std::basic_ostream<CharType>& s)

single_include/nlohmann/json.hpp

@@ -13485,11 +13485,11 @@ template<typename CharType>
 using output_adapter_t = std::shared_ptr<output_adapter_protocol<CharType>>;
 
 /// output adapter for byte vectors
-template<typename CharType>
+template<typename CharType, typename AllocatorType = std::allocator<CharType>>
 class output_vector_adapter : public output_adapter_protocol<CharType>
 {
   public:
-    explicit output_vector_adapter(std::vector<CharType>& vec) noexcept
+    explicit output_vector_adapter(std::vector<CharType, AllocatorType>& vec) noexcept
         : v(vec)
     {}
 
@@ -13505,7 +13505,7 @@ class output_vector_adapter : public output_adapter_protocol<CharType>
     }
 
   private:
-    std::vector<CharType>& v;
+    std::vector<CharType, AllocatorType>& v;
 };
 
 #ifndef JSON_NO_IO
@@ -13562,8 +13562,9 @@ template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_adapter
 {
   public:
-    output_adapter(std::vector<CharType>& vec)
-        : oa(std::make_shared<output_vector_adapter<CharType>>(vec)) {}
+    template<typename AllocatorType = std::allocator<CharType>>
+    output_adapter(std::vector<CharType, AllocatorType>& vec)
+        : oa(std::make_shared<output_vector_adapter<CharType, AllocatorType>>(vec)) {}
 
 #ifndef JSON_NO_IO
     output_adapter(std::basic_ostream<CharType>& s)

test/src/unit-regression2.cpp

@@ -181,6 +181,13 @@ class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json>
 
 std::string* sax_no_exception::error_string = nullptr;
 
+/////////////////////////////////////////////////////////////////////
+// for #2982
+/////////////////////////////////////////////////////////////////////
+
+template<class T>
+class my_allocator : public std::allocator<T>
+{};
 
 TEST_CASE("regression tests 2")
 {
@@ -679,6 +686,15 @@ TEST_CASE("regression tests 2")
         test3[json::json_pointer(p)] = json::object();
         CHECK(test3.dump() == "{\"/root\":{}}");
     }
+
+    SECTION("issue #2982 - to_{binary format} does not provide a mechanism for specifying a custom allocator for the returned type")
+    {
+        std::vector<std::uint8_t, my_allocator<std::uint8_t>> my_vector;
+        json j = {1, 2, 3, 4};
+        json::to_cbor(j, my_vector);
+        json k = json::from_cbor(my_vector);
+        CHECK(j == k);
+    }
 }
 
 DOCTEST_CLANG_SUPPRESS_WARNING_POP