Can style subobjects of a object differently, by key

include/nlohmann/detail/output/fancy_serializer.hpp

@@ -36,14 +36,16 @@ struct fancy_serializer_style
 };
 
 template<typename BasicJsonType>
-class fancy_serializer_stylizer
+class basic_fancy_serializer_stylizer
 {
   public:
-    fancy_serializer_stylizer(fancy_serializer_style const& ds)
+    using string_t = typename BasicJsonType::string_t;
+
+    basic_fancy_serializer_stylizer(fancy_serializer_style const& ds)
         : default_style(ds)
     {}
 
-    fancy_serializer_stylizer() = delete;
+    basic_fancy_serializer_stylizer() = default;
 
   public:
     const fancy_serializer_style& get_default_style() const
@@ -51,8 +53,26 @@ class fancy_serializer_stylizer
         return default_style;
     }
 
+    fancy_serializer_style& get_default_style()
+    {
+        return default_style;
+    }
+
+    const fancy_serializer_style& get_style(const string_t& j) const
+    {
+        auto iter = key_styles.find(j);
+        return iter == key_styles.end() ? default_style : iter->second;
+    }
+
+    fancy_serializer_style& get_or_insert_style(const string_t& j)
+    {
+        return key_styles[j];
+    }
+
   private:
     fancy_serializer_style default_style;
+
+    std::map<string_t, fancy_serializer_style> key_styles;
 };
 
 namespace detail
@@ -64,7 +84,7 @@ namespace detail
 template<typename BasicJsonType>
 class fancy_serializer
 {
-    using stylizer_t = fancy_serializer_stylizer<BasicJsonType>;
+    using stylizer_t = basic_fancy_serializer_stylizer<BasicJsonType>;
     using primitive_serializer_t = primitive_serializer<BasicJsonType>;
     using string_t = typename BasicJsonType::string_t;
     using number_float_t = typename BasicJsonType::number_float_t;
@@ -216,7 +236,8 @@ class fancy_serializer
             o->write_character('\"');
             prim_serializer.dump_escaped(*o, i->first, ensure_ascii);
             o->write_characters("\": ", 2 + newline_len);
-            dump(i->second, ensure_ascii, depth + 1, active_style);
+            auto new_style = &stylizer.get_style(i->first);
+            dump(i->second, ensure_ascii, depth + 1, new_style);
             o->write_characters(",\n", 1 + newline_len);
         }
 
@@ -227,7 +248,8 @@ class fancy_serializer
         o->write_character('\"');
         prim_serializer.dump_escaped(*o, i->first, ensure_ascii);
         o->write_characters("\": ", 2 + newline_len);
-        dump(i->second, ensure_ascii, depth + 1, active_style);
+        auto new_style = &stylizer.get_style(i->first);
+        dump(i->second, ensure_ascii, depth + 1, new_style);
 
         o->write_characters("\n", newline_len);
         o->write_characters(indent_string.c_str(), old_indent);
@@ -360,13 +382,20 @@ class fancy_serializer
 
 template<typename BasicJsonType>
 std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
-                         fancy_serializer_style style)
+                         basic_fancy_serializer_stylizer<BasicJsonType> const& stylizer)
 {
-    fancy_serializer_stylizer<BasicJsonType> stylizer(style);
     // do the actual serialization
     detail::fancy_serializer<BasicJsonType> s(detail::output_adapter<char>(o), stylizer);
     s.dump(j, false);
     return o;
 }
 
+template<typename BasicJsonType>
+std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
+                         fancy_serializer_style style)
+{
+    basic_fancy_serializer_stylizer<BasicJsonType> stylizer(style);
+    return fancy_dump(o, j, stylizer);
+}
+
 }

include/nlohmann/json.hpp

@@ -7624,6 +7624,8 @@ class basic_json
 
     /// @}
 };
+
+using fancy_serializer_stylizer = basic_fancy_serializer_stylizer<json>;
 } // namespace nlohmann
 
 ///////////////////////

single_include/nlohmann/json.hpp

@@ -10106,14 +10106,16 @@ struct fancy_serializer_style
 };
 
 template<typename BasicJsonType>
-class fancy_serializer_stylizer
+class basic_fancy_serializer_stylizer
 {
   public:
-    fancy_serializer_stylizer(fancy_serializer_style const& ds)
+    using string_t = typename BasicJsonType::string_t;
+
+    basic_fancy_serializer_stylizer(fancy_serializer_style const& ds)
         : default_style(ds)
     {}
 
-    fancy_serializer_stylizer() = delete;
+    basic_fancy_serializer_stylizer() = default;
 
   public:
     const fancy_serializer_style& get_default_style() const
@@ -10121,8 +10123,26 @@ class fancy_serializer_stylizer
         return default_style;
     }
 
+    fancy_serializer_style& get_default_style()
+    {
+        return default_style;
+    }
+
+    const fancy_serializer_style& get_style(const string_t& j) const
+    {
+        auto iter = key_styles.find(j);
+        return iter == key_styles.end() ? default_style : iter->second;
+    }
+
+    fancy_serializer_style& get_or_insert_style(const string_t& j)
+    {
+        return key_styles[j];
+    }
+
   private:
     fancy_serializer_style default_style;
+
+    std::map<string_t, fancy_serializer_style> key_styles;
 };
 
 namespace detail
@@ -10134,7 +10154,7 @@ namespace detail
 template<typename BasicJsonType>
 class fancy_serializer
 {
-    using stylizer_t = fancy_serializer_stylizer<BasicJsonType>;
+    using stylizer_t = basic_fancy_serializer_stylizer<BasicJsonType>;
     using primitive_serializer_t = primitive_serializer<BasicJsonType>;
     using string_t = typename BasicJsonType::string_t;
     using number_float_t = typename BasicJsonType::number_float_t;
@@ -10286,7 +10306,8 @@ class fancy_serializer
             o->write_character('\"');
             prim_serializer.dump_escaped(*o, i->first, ensure_ascii);
             o->write_characters("\": ", 2 + newline_len);
-            dump(i->second, ensure_ascii, depth + 1, active_style);
+            auto new_style = &stylizer.get_style(i->first);
+            dump(i->second, ensure_ascii, depth + 1, new_style);
             o->write_characters(",\n", 1 + newline_len);
         }
 
@@ -10297,7 +10318,8 @@ class fancy_serializer
         o->write_character('\"');
         prim_serializer.dump_escaped(*o, i->first, ensure_ascii);
         o->write_characters("\": ", 2 + newline_len);
-        dump(i->second, ensure_ascii, depth + 1, active_style);
+        auto new_style = &stylizer.get_style(i->first);
+        dump(i->second, ensure_ascii, depth + 1, new_style);
 
         o->write_characters("\n", newline_len);
         o->write_characters(indent_string.c_str(), old_indent);
@@ -10430,15 +10452,22 @@ class fancy_serializer
 
 template<typename BasicJsonType>
 std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
-                         fancy_serializer_style style)
+                         basic_fancy_serializer_stylizer<BasicJsonType> const& stylizer)
 {
-    fancy_serializer_stylizer<BasicJsonType> stylizer(style);
     // do the actual serialization
     detail::fancy_serializer<BasicJsonType> s(detail::output_adapter<char>(o), stylizer);
     s.dump(j, false);
     return o;
 }
 
+template<typename BasicJsonType>
+std::ostream& fancy_dump(std::ostream& o, const BasicJsonType& j,
+                         fancy_serializer_style style)
+{
+    basic_fancy_serializer_stylizer<BasicJsonType> stylizer(style);
+    return fancy_dump(o, j, stylizer);
+}
+
 }
 
 // #include <nlohmann/detail/json_ref.hpp>
@@ -18811,6 +18840,8 @@ class basic_json
 
     /// @}
 };
+
+using fancy_serializer_stylizer = basic_fancy_serializer_stylizer<json>;
 } // namespace nlohmann
 
 ///////////////////////

test/src/unit-fancy-serialization.cpp

@@ -34,6 +34,7 @@ SOFTWARE.
 using nlohmann::json;
 using nlohmann::fancy_dump;
 using nlohmann::fancy_serializer_style;
+using nlohmann::fancy_serializer_stylizer;
 
 // Chops off the first line (if empty, but if it *isn't* empty you're
 // probably using this wrong), measures the leading indent on the
@@ -77,6 +78,13 @@ std::string fancy_to_string(json j, fancy_serializer_style style = fancy_seriali
     return ss.str();
 }
 
+std::string fancy_to_string(json j, fancy_serializer_stylizer stylizer)
+{
+    std::stringstream ss;
+    fancy_dump(ss, j, stylizer);
+    return ss.str();
+}
+
 TEST_CASE("serialization")
 {
     SECTION("primitives")
@@ -220,6 +228,36 @@ TEST_CASE("serialization")
         }
     }
 
+    SECTION("changing styles")
+    {
+        SECTION("can style objects of a key differently")
+        {
+            fancy_serializer_stylizer stylizer;
+            stylizer.get_default_style().indent_step = 4;
+            stylizer.get_or_insert_style("one line").indent_step = 0;
+
+            auto str = fancy_to_string(
+            {
+                {
+                    "one line", {1, 2}
+                },
+                {
+                    "two lines", {1, 2}
+                }
+            },
+            stylizer);
+
+            CHECK(str == dedent(R"(
+                {
+                    "one line": [1,2],
+                    "two lines": [
+                        1,
+                        2
+                    ]
+                })"));
+        }
+    }
+
     SECTION("given width")
     {
         fancy_serializer_style style;